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

#include <iostream>
#include <stdlib.h>

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;
    
    if(goal.x > goal.y) {
        te = abs(goal.x);
    }
    else {
        te = abs(goal.y);
    }
    
    if(block.x == block.y && goal.x == goal.y && block.x < goal.x) {
        te++;
    }
    
    std::cout << te << "\n";
    return 0;
}