/* -*- coding: utf-8 -*-
 *
 * 208.cc: No.208 王将 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int x, y, x2, y2;
  cin >> x >> y >> x2 >> y2;

  int ax = abs(x), ay = abs(y), ax2 = abs(x2), ay2 = abs(y2);
  
  int ans = max(ax, ay);
  if (ax == ay && ax2 == ay2 && ax2 < ax && x * x2 > 0 && y * y2 > 0)
    ans++;

  printf("%d\n", ans);
  return 0;
}