#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using T = tuple<int, int, int>;
#define al(a) a.begin(), a.end()
#define ral(a) a.rbegin(), a.rend()
#define sz(a) (int)a.size()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define db(a, b) cout << #a << ": " << a << " " << #b << ": " << b << endl;

int main() {
  ll x, y, x2, y2;
  cin >> x >> y >> x2 >> y2;
  int ans = max(x, y);
  //   if (y2 * x == y * x2) ans++;
  if (abs(x) == abs(y) && abs(x2) == abs(y2) && abs(x) > abs(x2) &&
      abs(y) > abs(y2) && x / abs(x) == x2 / abs(x2) &&
      y / abs(y) == y2 / abs(y2))
    ans++;
  cout << ans << endl;
  return 0;
}