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