#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;

#define pb push_back

const ld pi = 3.14159265358979323846;
const int mod = (int)1e9 + 7;
const ll INF = 1e18;

template<typename T>
T chmax(T a, T b) {
    return a > b ? a : b;
}

template<typename T>
T chmin(T a, T b) {
    return a > b ? b : a;
}

const int N = (int)2e5 + 1, M = N * 2;

void solve() {
    int ds, ys, dm, ym;
    cin >> ds >> ys >> dm >> ym;

    int year = 0;
    while(1){
        if((year + ds) % ys == 0 && (year + dm) % ym == 0) {
            cout << year << '\n';
            break;
        }
        year++;
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(0);

    int t = 1;
    // cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}