#define _CRT_SECURE_NO_WARNINGS
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#include <stack>
#include <array>
#include <fstream>
#include <deque>

#define REP(i,n) for(int (i) = 0;(i) < (n) ; ++(i))
#define REPA(a,i,n) for(int (i) = (a) ; (i) < (n) ; ++(i))
#if defined(_MSC_VER)||__cplusplus > 199711L
#define AUTO(r,v) auto r = (v)
#else
#define AUTO(r,v) typeof(v) r = (v)
#endif
#define ALL(c) (c).begin() , (c).end()
#define EACH(it,c) for(AUTO(it,(c).begin());it != (c).end();++it)
#define LL long long
#define int LL
#define INF  99999999
#define DEV 1000000007
#define QUICK_CIN ios::sync_with_stdio(false); cin.tie(0);

template<class T>
bool valid(T x, T w){ return 0 <= x&&x < w; }

int di[4] = { 1, -1, 0, 0 };
int dj[4] = { 0, 0, 1, -1 };

using namespace std;

//-----------------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------------
//-----------------------------------------------------------------------------------------------

int x, y, x2, y2;


signed main()
{
    QUICK_CIN;
    //ifstream cin("debug.txt");
    //ofstream cout("result.txt");

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

    int temp = 0;

    if (x > 0 && x == y){
        if (x2 > 0 && x2 == y2 && x2 < x){
            temp++;
        }
    }

    if (x < 0 && x == y){
        if (x2 < 0 && x2 == y2 && x2 > x){
            temp++;
        }
    }

    if (x > 0 && x == -y){
        if (x2 > 0 && x2 == -y2 && x2 < x){
            temp++;
        }
    }

    if (x < 0 && x == -y){
        if (x2 < 0 && x2 == -y2 && x2 > x){
            temp++;
        }
    }

    int ans = min(x, y);
    x -= ans;
    y -= ans;
    ans += x + y + temp;

    cout << ans << endl;

    return 0;
}