#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <limits.h>
using namespace std;


int main(){
	int goal[2];
	int teki[2];
	int goal_h[2];
	int teki_h[2];
	int adjust = 0;
	
	cin >> goal[0] >> goal[1] >> teki[0] >> teki[1];
	
	//斜め
	if(abs(goal[0]) == abs(goal[1]) && abs(teki[0]) == abs(teki[1]) ){
		//符号調査
		for(int i=0; i<2; i++){
			if(goal[i] == 0){
				goal_h[i] = 0;
			}else if(goal[i] < 0){
				goal_h[i] = -1;
			}else{
				goal_h[i] = 1;
			}
		}
		for(int i=0; i<2; i++){
			if(teki[i] == 0){
				teki_h[i] = 0;
			}else if(teki[i] < 0){
				teki_h[i] = -1;
			}else{
				teki_h[i] = 1;
			}
		}
		
		
		//斜め
		if(goal_h[0] == teki_h[0] && goal_h[1] == teki_h[1] && abs(teki[0]) < abs(goal[0]) && abs(teki[1]) < abs(goal[1])){
			adjust = 1;
		}else{
			adjust = 0;
		}
	}else{
		adjust = 0;
	}
	
	cout << max(abs(goal[0]), abs(goal[1])) + adjust << endl;
	return 0;
}