#include <stdio.h>
#include <stdlib.h>

int main(){
    long a_x, a_y, b_x, b_y;
    scanf("%ld %ld %ld %ld", &a_x, &a_y, &b_x, &b_y);
    double time_x, time_y;
    time_x = (double)labs(a_x - b_x);
    time_y = (double)labs(a_y - b_y);
    if(time_x < time_y){
        printf("%d\n", time_x);
    }else{
        printf("%d\n", time_y);
    }
    return 0;
}