#include<bits/stdc++.h>
using namespace std;
	
int main(){
	double x1,y1,x2,y2;
	cin>>x1>>y1>>x2>>y2;
	printf("%.2lf",sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)));
	return 0;
}