import std;

void main () {
    /* 後でちゃんと解く(多分)今は全探索 */
    int A, B, a, b; readln.read(A, B, a, b);

    int ans = a;
    while (true) {
        if (ans % B == b) break;
        ans += A;
    }

    writeln(ans);
}

void read (T...) (string S, ref T args) {
    auto buf = S.split;
    foreach (i, ref arg; args) {
        arg = buf[i].to!(typeof(arg));
    }
}