#include <cstdio>
#include <algorithm>
using namespace std;

int sign(int n) { return (n>0) - (n<0); }

int main(void) {
  int x, y, x2, y2;
  int res;
  scanf("%d%d%d%d", &x, &y, &x2, &y2);
  if(y==0 && y2==0 && sign(x)==sign(x2) && abs(x)>abs(x2)) { res = abs(x); }
  else if(x==0 && x2==0 && sign(y)==sign(y2) && abs(y)>abs(y2)) { res = abs(y); }
//  else if(x==0 || x2==0 || y==0||y2==0) { res=max(abs(x), abs(y)); }
  else if(x==y && x2==y2 && sign(x)==sign(x2) && abs(x)>abs(x2)) { res = abs(x) + 1; }
  else if(x==-y && x2==-y2 && sign(x)==sign(x2) && abs(x)>abs(x2)) { res = abs(x) + 1; }
  else { res = max(abs(x), abs(y)); }
  printf("%d\n", res);
  return 0;
}