/**
 * @file 2558.cpp
 * @brief yukicoder problem 2558
 * @author Keitaro Naruse
 * @date 2023-12-02
 * @copyright MIT License
 * @details https://yukicoder.me/problems/no/2558
 * */

// # Solution

#include <iostream>

int main( ) {
    //  Read A, B = [ 1, 3*10^3 ], a = [ 0, A ), b = [ 0, B )
    int A, B, a, b;
    std::cin >> A >> B >> a >> b;

    //  Main::Preprocess
    //  Main::Find a solution
    int answer = 0;
    for( int x = 0; x < A * B; x++ ) {
        if( x % A == a && x % B == b ) {
            answer = x;
            break;
        }
    }
    //  Main::Output a solution
    std::cout << answer << std::endl;
    //  Finalize
    return 0;
}