// Arup Guha
// 2/25/2023
// Solution to 2022 SER D2 Problem: Sun and Moon

using namespace std;

#include <iostream>

int main() {

    // Read mod info.
    int prev1, cycle1;
    int prev2, cycle2;
    cin >> prev1 >> cycle1;
    cin >> prev2 >> cycle2;

    // Just brute force it.
    for (int i=1; i<=5000; i++) {
        if (i%cycle1 == (cycle1-prev1)%cycle1 &&
            i%cycle2 == (cycle2-prev2)%cycle2) {
                cout << i << endl;
                break;
            }
    }

    return 0;
}