include <bits/stdc++.h>

using namespace std; int main() {

float x1,y1,x2,y2;
int z;
scanf("%f%f%f%f",&x1,&y1,&x2,&y2);
z=sqrt(pow(x1-x2,2)+pow(y1-y2,2));
cout<<z;
return 0;

}