#include<bits/stdc++.h> using namespace std; int main() { double Xa,Ya,Xb,Yb; scanf("%lf%lf%lf%lf",&Xa,&Ya,&Xb,&Yb); printf("%.3f",sqrt((Xb-Xa)(Xb-Xa)+(Yb-Ya)(Yb-Ya))); return 0; }