//
//  main.cpp
//  Q487
//
//  Created by AkihiroKOBAYASHI on 7/11/15.
//  Copyright (c) 2015 Akhr5884. All rights reserved.
//

#include <iostream>

struct Point {
    int x;
    int y;
};

int main(int argc, const char * argv[]) {
    
    Point start, block, goal;
    int te;
    
    start.x = start.y = 0;
    std::cin >> goal.x;
    std::cin >> goal.y;
    std::cin >> block.x;
    std::cin >> block.y;
    
    te = (goal.x-start.x) + (goal.y-start.y) -1;
    
    std::cout << te << "\n";
    return 0;
}