#include<bits/stdc++.h> using namespace std; #define ll long long double x1,x2,a1,a2,dis; int main(void) { scanf("%lf%lf%lf%lf",&x1,&a1,&x2,&a2); dis=sqrt((x2-x1)*(x2-x1)+(a2-a1)*(a2-a1)); printf("%.4lf\n",dis); return 0; }