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

int main(){
	int goaly,goalx;
	int tekiy,tekix;
	int goaly_h,goalx_h;
	int tekiy_h,tekix_h;
	
	cin >> goalx >> goaly >> tekix >> tekix;
	
	if(abs(goaly) != abs(goalx)){
		cout << max(abs(goaly), abs(goalx)) << endl;
	}else{
		//符号調査
		if(goaly < 0){
			goaly_h = -1;
		}else{
			goaly_h = 1;
		}
		if(goalx < 0){
			goalx_h = -1;
		}else{
			goalx_h = 1;
		}
		if(tekiy < 0){
			tekiy_h = -1;
		}else{
			tekiy_h = 1;
		}
		if(tekix < 0){
			tekix_h = -1;
		}else{
			tekix_h = 1;
		}
		
		if(abs(tekiy) == abs(tekix) && goaly_h == tekiy_h && goalx_h == tekix_h){
			cout << max(abs(goaly), abs(goalx)) + 1 << endl;
		}else{
			cout << max(abs(goaly), abs(goalx)) << endl;
		}
	}
	
	return 0;
}