#include <bits/stdc++.h>
#define fi first
#define se second
#define bit(x) (1LL << (x))
#define getbit(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x.begin(), x.end())
using namespace std;

template <typename T1, typename T2> bool maxi(T1 &a, T2 b) {
    if (a < b) {a = b; return true;} return false;
}

template <typename T1, typename T2> bool mini(T1 &a, T2 b) {
    if (a > b) {a = b; return true;} return false;
}

const int N = 2e5 + 5;
const int oo = 1e9;
const long long ooo = 1e18;


int main() {
    int a, b;
    int c, d;
    cin >> a >> b >> c >> d;
    int curb = b-a;
    int curd = d-c;
    for(int i = 1; i <= 100; i++)
    {
        // cout << curb << " " << curd << "\n";
        curb--;
        curd--;
        if(curb == 0 && curd == 0)
        {
            cout << i << '\n';
            return 0;
        }
        if(curb == 0) curb = b;
        if(curd == 0) curd = d;
    }
}