#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
    double x1,y1,x2,y2;
    double result;
    while (cin>>x1>>y1>>x2>>y2)
    {
        result = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        cout << setprecision(2) << setiosflags(ios::fixed) << result << endl;
    }
    return 0;
}