#include <stdio.h>
#include<math.h>
#include <stdlib.h>
int main()
{
    int x1,y1 = 0;
    int x2,y2 = 0;
    double de = 0;
    double dm = 0;
    double sum = 0;
    scanf("%d %d %d %d",&x1,&y1,&x2,&y2);
    de = sqrt(pow(x1-x2,2) +  pow(y1-y2,2));
    dm = abs(x1 - x2) + abs(y1 - y2);
    sum = fabs(dm - de);
    printf("%lf",sum);
    return 0;
}