#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<ctime>
#include<complex>
#include<functional>
#include<climits>
#include<cassert>
#include<iterator>
using namespace std;

int main(){
	long long int x, y, x2, y2;
	scanf("%lld%lld%lld%lld", &x, &y, &x2, &y2);
	long long int ans = abs(x2 - x) + abs(y2 - y);
	printf("%lld\n", ans);
	return 0;
}