#include <bits/stdc++.h>
using namespace std;

signed main(){
  int X, Y; cin >> X >> Y;
  int X2, Y2; cin >> X2 >> Y2;
  int ans = max( X, Y );
  if( abs( X ) == abs( Y ) and abs( X2 ) == abs( Y2 ) and X2 < X )
    if( 1LL * X * X2 > 0 and 1LL * Y * Y2 > 0 )
      ++ans;
  cout << ans << endl;
  return 0;
}