#include<bits/stdc++.h>
using namespace std;
int main()
{
	double x1,x2,y1,y2;
	cin>>x1>>x2>>y1>>y2;
	cout<<fixed<<setprecision(3)<<sqrt(pow(abs(x1-x2),2)+pow(abs(y1-y2),2))<<endl;
	return 0;
}