#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main() {
    int x1, y1, x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    double e;
    int m;
    double dx = x1 - x2;
    double dy = y1 - y2;
    e = sqrt(dx * dx + dy * dy);
    m = abs(dx) + abs(dy);
    cout << fixed << setprecision(10) << fabs(m - e) << endl;
}
// 64 位输出请用 printf("%lld")