#include<bits/stdc++.h>
using namespace std;
int main(){
    double x1,x2,y1,y2,ans;cin>>x1>>x2>>y1>>y2;
    ans=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
    printf("%.3f",ans);
    return 0;
}