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

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
	double xa,xb,ya,yb,l;
	cin >> xa >> ya >> xb >> yb;
	l = sqrt(pow(xa-xb,2)+pow(ya-yb,2));
	printf("%.3lf",l);
	return 0;
}