//Test1
#include <iostream.h>
#include <math.h>
#include <cstdio>
double main(){
int x1,y1,x2,y2;
double result;
double sum[100];
int n=1;
while(cin>>x1>>y1>>x2>>y2 )
{
if(x1==0 && x2==0 && y1==0 && y2==0)
{
for(int z=1;z<n;z++)
{
cout.setf(ios::fixed);
cout.precision(2);
cout<<sum[z]<<endl;
}
}
int x=x2-x1;
int y=y2-y1;
result=sqrt(x*x+y*y);
sum[n]=result;
n++;
}
return 0;
}
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//Test2
import java.util.Scanner;
public class test2 {
static int sum;
public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
String Date=scan.nextLine();
int year=Integer.parseInt(Date.substring(0, 4));
int month=Integer.parseInt(Date.substring(5, 7));
int day=Integer.parseInt(Date.substring(8, 10));
count(year,month,day);
}
static int count(int yy,int mm,int dd){
if(yy==1){
sum=dd;
}
else
{
sum=dd;
mm=mm-1;
switch(mm){
case 1: sum+=31;
break;
case 2: sum+=60;
break;
case 3: sum+=91;
break;
case 4: sum+=121;
break;
case 5: sum+=152;
break;
case 6: sum+=182;
break;
case 7: sum+=213;
break;
case 8: sum+=244;
break;
case 9: sum+=274;
break;
case 10: sum+=305;
break;
case 11: sum+=335;
break;
}
}
if(runNian(yy)){
sum-=1;
}
System.out.println(sum);
return 0;
}
static boolean runNian(int year)//判断是否为闰年的方法
{
boolean t=false;
if(year%4==0)
{
if(year%100!=0)
{
t=true;
}
else if(year%400==0)
{
t=true;
}
}
return t;
}
}
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//Test3
import java.util.Scanner;
public class Test3 {
public static void main(String[] args) {
int ou=0;
int ji=0;
Scanner scan=new Scanner(System.in);
int a=scan.nextInt();
int b=scan.nextInt();
//int tt[]=new int[b-a+1];
for(int i=a;i<=b;i++){
if(i%2==0){
ou+=i*i;
}else
ji+=i*i*i;
}
System.out.print(ou+" "+ji);
}
}
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//Test4
import java.util.Scanner;
public class Test4 {
public static void main(String[] args) {
while(true){
Scanner scan=new Scanner(System.in);
int a=scan.nextInt();
int b=scan.nextInt();
int sum=0;
for(int i=a;i<=b;i++){
int bai=i/100;
int shi=(i-bai*100)/10;
int ge=i-bai*100-shi*10;
if(bai*bai*bai+shi*shi*shi+ge*ge*ge==i){
System.out.print(i+" ");
sum++;
}
}
if(sum==0)
{
System.out.print("No!");
}
}
}
}
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//Test5
import java.util.Scanner;
public class Test5 {
static double sum=0;
public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
int N=scan.nextInt();
int[] Nn=new int[N];
double[] Nsum=new double[N];
for(int i=0;i<N;i++){
Nn[i]=scan.nextInt();
}
for(int i=0;i<Nn.length;i++)
{
int D=Nn[i];
for(int z=1;z<=D;z++)
{
if(z%2==0){
sum-=((double)1/(double)z);
}else{
sum+=((double)1/(double)z);
}
}
Nsum[i]=sum;
sum=0;
}
for(int i=0;i<N;i++){
System.out.print(Nsum[i]+" ");
}
}
}
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//Test6
import java.util.Scanner;
public class Test6 {
public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
int number=0;
int m=0,n=0;
boolean tt[]=new boolean[50];
boolean flag=true;
boolean flag2=true;
while(flag){
flag2=true;
n=scan.nextInt();
m=scan.nextInt();
if(m==0&&n==0){
flag=false;
for(int i=0;i<number;i++){
if(tt[i]){
System.out.println("OK");
}else{
System.out.println("Sorry");
}
}
break;
}
if(n>m){
int temp=0;
temp=m;
m=n;
n=temp;
}
for(int i=n;i<=m;i++){
if(!isPrimes(i)){
flag2=false;
break;
}
}
if(flag2){
tt[number]=true;
number++;
}else
{
tt[number]=false;
number++;
}
}
}
public static boolean isPrimes(int n) {
for (int i = 2; i <= Math.sqrt(n); i++) {
if (n % i == 0) {
return false;
}
}
return true;
}
}
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//Test7
import java.util.Scanner;
public class Test7 {
public static void main(String[] args) {
int sum=1;
Scanner scan=new Scanner(System.in);
int n=scan.nextInt();
for(int i=n;i>1;i--){
sum=(sum+1)*2;
}
System.out.println(sum);
}
}
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//Test8
import java.util.Scanner;
public class Test8 {
public static void main(String[] args) {
int cow=1;
int xcow=0;
Scanner scan=new Scanner(System.in);
int n=scan.nextInt();
for(int i=1;i<=n;i++){
if(i%4==0){
xcow--;
cow++;
}
xcow+=cow;
}
System.out.println(xcow);
}
}
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//Test9
public class Test9 {
public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
int sum=0;
int n=scan.nextInt();
int[] tt=new int[n];
for(int i=0;i<n;i++){
tt[i]=scan.nextInt();
}
for(int i=0;i<n;i++){
int z=tt[i];
sum=jisuan(z);
System.out.println(sum);
}
}
static int jisuan(int i){
int sum=0;
if(i>=100){
sum+=i/100;
i=i%100;
}if(i>=50){
sum+=i/50;
i=i%50;
}if(i>=10){
sum+=i/10;
i=i%10;
}if(i>=5){
sum+=i/5;
i=i%5;
}if(i>=2){
sum+=i/2;
i=i%2;
}if(i>=1){
sum+=i/1;
}
return sum;
}
}
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//Test10
import java.util.Scanner;
public class Test10 {
public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
int n=scan.nextInt();
boolean[] tt=new boolean[n];
for(int i=0;i<n;i++){
boolean tz=true;
String str=scan.next();
char[] strChar = str.toCharArray();
int number=strChar.length;
for(int z=0;z<number;z++){
if(strChar[z]!=strChar[number-z-1]){
tz=false;
}
}
tt[i]=tz;
}
for(int i=0;i<n;i++){
System.out.println(tt[i]);
}
}
}
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//Test11
import java.util.Scanner;
public class Test11 {
public static void main(String[] args) {
int sum=1;
Scanner scan=new Scanner(System.in);
int n=scan.nextInt();
int tt[]=new int[n];
for(int i=0;i<n;i++){
sum=1;
int a=scan.nextInt();
int b=scan.nextInt();
for(int z=0;z<b;z++){
sum*=a;
}
tt[i]=sum;
}
for(int i=0;i<n;i++){
sum=tt[i];
if(sum>=100){
sum=sum%1000;
}
System.out.print(sum+" ");
}
}
}
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