#include <bits/stdc++.h>
using namespace std;

int main(){
	int a,b,c,d; cin >> a >> b >> c >> d;
	assert(a>0&&a<3001);
	assert(b>0&&b<3001);
	assert(c>-1&&c<a);
	assert(d>-1&&d<b);
	assert(gcd(a,b)==1);
	while(c%b!=d) c+=a;
	cout << c << endl;
}