#include<bits/stdc++.h>
using namespace std;              
int main()
{
    int xa,xb,ya,yb;
    cin>>xa>>ya>>xb>>yb;
    printf("%.3lf",sqrt((max(xa,xb)-min(xa,xb))*(max(xa,xb)-min(xa,xb))+(max(ya,yb)-min(ya,yb))*(max(ya,yb)-min(ya,xb))));
	return 0;
}