#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>
#include <time.h>
using namespace std;
//#define int long long
#define rep(i,s,n) for(int i = s;i<n;i++)
#define repe(i,s,n) for(int i = s;i<=n;i++)
#define rrep(i,s,n) for(int i = (n)-1;i>=(s);i--)
#define all(v) (v).begin(),(v).end()
#define pb push_back
#define fi first
#define se second
#define chmin(a,b) a=min((a),(b))
#define chmax(a,b) a=max((a),(b))
#define l1 list[index]
#define l2 list[index - 1]
#define l3 list[index + 1]
#define iif(i,j) ((i<0 && j<0) || (i>0 && j>0)) ? true : false 
typedef long long ll;
typedef pair<int, int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
typedef pair<pint, int> P1;
typedef pair<int, pint> P2;
typedef pair<pint, pint> PP;
static const ll maxLL = (ll)1 << 62;
const ll MOD = 1000000007;
const ll INF = 1e18;
int ca[12] = { 31,28,31,30,31,30,31,31,30,31,30,31 };



signed main() {
	string s;
	int n, k, cnt = 0;
	vector<int>list(10005, 99999999);
	ll x, y, x2, y2;
	int flag1, flag2;

	cin >> x >> y >> x2 >> y2;

	if (x >= 0 && y >= 0)flag1 = 0;
	if (x >= 0 && y <= 0)flag1 = 1;
	if (x <= 0 && y >= 0)flag1 = 2;
	if (x <= 0 && y <= 0)flag1 = 3;

	if (x2 >= 0 && y2 >= 0)flag2 = 0;
	if (x2 >= 0 && y2 <= 0)flag2 = 1;
	if (x2 <= 0 && y2 >= 0)flag2 = 2;
	if (x2 <= 0 && y2 <= 0)flag2 = 3;



	if ((abs(x) == abs(y) && abs(x2) == abs(y2) && flag1 == flag2 && abs(x) > abs(x2) ) ) {
		cout << abs(x) + 1 << endl;
	}
	else {
		cout << max(abs(x), abs(y)) << endl;
	}
	/*if ((x == 0 && x2 == 0 && y > y2) || (y == 0 && y2 == 0 && x > x2)) {

	}*/











	getchar();
	getchar();
	return 0;
}