HDU2001

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<cmath>
using namespace std;

int main()
{
    double a, b, x, y;
    while(scanf("%lf %lf %lf %lf",&a,&b,&x,&y)!=EOF)
    {
        double x1 ,x2;
        x1 = fabs(x - a);
        x2 = fabs(y - b);
        double ans;
        ans = sqrt(x1*x1 + x2*x2);
        printf("%.2lf\n",ans);
    }
}