#include <stdio.h>
#include<math.h>

int main()
{
    int x1, y1;
    scanf("%d %d", &x1, &y1);
    int x2, y2;
    scanf("%d %d", &x2, &y2);
    double dE = sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2));
    double dM = fabs(x1 - x2) + fabs(y1 - y2);
    double s = fabs(dM - dE);
    printf("%lf", s);
    return 0;
}