#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <algorithm>
#include <set>
#include <sstream>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <climits>
#include <iostream>
#include <iomanip>
#include <functional>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(int x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int main()
{
    ll x,y,x2,y2;
    cin >> x >> y;
    cin >> x2 >> y2;
    
    if(x * y2 == y * x2)
    {
        if(abs(x) == abs(y))
        {
            if(abs(x) > abs(x2))
            {
                cout << abs(x) + 1 << endl;
                return 0;
            }
        }
    }
    cout << max(abs(x), abs(y)) << endl;
    return 0;
}