#define _USE_MATH_DEFINES
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<climits>
#include<string>
#include<vector>
#include<list>
#include<map>
#include<set>
#include<cmath>
#include<queue>
#include<cstring>
#include<stack>
#include<functional>
#include<deque>
#include<cstdlib>
#include<ctime>
using namespace std;

int main(){
	int X,Y,X2,Y2;
	cin>>X>>Y>>X2>>Y2;
	int ans = max(abs(X2),abs(Y2));
	printf("%d\n",ans);
    return 0;
}