import std, core.bitop;
string[] _R;
void readM(T)(ref T x) { while (_R.empty) { _R = readln.chomp.split; } x = _R.front.to!T; _R.popFront; }
bool chmin(T)(ref T A, T B) { return (A > B ? A = B, true : false); }
bool chmax(T)(ref T A, T B) { return (A < B ? A = B, true : false); }
int lowerBound(T)(T[] A, T x) { int lo = -1, hi = cast(int)(A.length); while (hi - lo > 1) { int mid = lo + hi >> 1; (A[mid] < x ? lo : hi) = mid; } return hi; }
int upperBound(T)(T[] A, T x) { int lo = -1, hi = cast(int)(A.length); while (hi - lo > 1) { int mid = lo + hi >> 1; (A[mid] > x ? hi : lo) = mid; } return hi; }

void main() {
	int A, B, a, b;
	A.readM;
	B.readM;
	a.readM;
	b.readM;
	foreach (i; 0 .. (10 ^^ 9)) {
		if (i % A == a && i % B == b) {
			writeln(i);
			break;
		}
	}
}