#include <stdio.h>
#include <math.h>

int main()
{
double x1,y1,x2,y2,distance;
scanf("%lf%lf%lf%lf", &x1,&y1,&x2,&y2);
distance = sqrt( (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) );

printf("%.3lf\n", distance);
return 0;
}

#include <stdio.h>
#include <math.h>

int main()
{
double x1,y1,x2,y2,distance;
scanf("%lf%lf%lf%lf", &x1,&y1,&x2,&y2);
distance = sqrt( (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) );

printf("%.3lf\n", distance);
return 0;
}

#include <stdio.h>
#include <math.h>

int main()
{
double x1,y1,x2,y2,distance;
scanf("%lf%lf%lf%lf", &x1,&y1,&x2,&y2);
distance = sqrt( (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2) );

printf("%.3lf\n", distance);
return 0;
}

#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int main()
{
double x1,y1,x2,y2,dis;
cin>>x1>>y1>>x2>>y2;
dis=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
cout<<fixed<<setprecision(3)dis<<endl;
return 0;
}