#include <cmath> #include <cstdio> #include <iostream> using namespace std; int main() { double x1,y1,x2,y2,d; cin>>x1>>y1; cin>>x2>>y2; d=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)); printf("%.4lf",d); return 0; }