#include<iostream>
#include<math.h>
struct point
{
    int x;
    int y;
};

double distance(point a, point b)
{
    return sqrt((b.y - a.y) * (b.x - a.x) + (b.x - a.x) * (b.x - a.x));
}

double max(double a, double b)
{
    if (a > b) return a;
    else return b;
}
int main()
{
    point a, b;
    double distance;

    std::cin >> a.x >> a.y;
    std::cin >> b.x >> b.y;
    distance = max(distance(a, b), distance(b, a));

    std::cout << distance;

}