#include <iostream>
#include <math.h>
using namespace std;
double distance(int *a, int *b, int *c, int *d){
    return sqrt(((*a-*c)*(*a-*c))+((*b-*d)*(*b-*d)));
}
int main() {
    int x1,y1,x2,y2;
    cin>>x1>>y1>>x2>>y2;
    int *a = &x1;
    int *b = &y1;
    int *c = &x2;
    int *d = &y2;
    cout<<distance(&x1,&y1,&x2,&y2);
}