#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF (1LL << 25) // 33554432
#define PI 3.14159265359
#define EPS 1e-12
//#define int ll

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

  if (abs(x) == abs(y)) {
    if ((x <= 0 && y <= 0 && x2 <= 0 && y2 <= 0) ||
        (x <= 0 && y >= 0 && x2 <= 0 && y2 >= 0) ||
        (x >= 0 && y <= 0 && x2 >= 0 && y2 <= 0) ||
        (x >= 0 && y >= 0 && x2 >= 0 && y2 >= 0)) {
      if(abs(x2) == abs(y2)) {
        cout << abs(x)+1 << endl;
        return 0;
      }
    }
    cout << abs(x) << endl;
    return 0;
  } else {
    cout << max(abs(x), abs(y)) << endl;
  }

  return 0;
}