#include "bits/stdc++.h"

using namespace std;

void solve()
{
	int a, b, c, d, ans = 0;
	cin >> a >> b >> c >> d;
	for (int x = 0; x <= a; x++)
	{
		if (x*c <= b && x*(c+1) <= d)
		{
			ans = x*(c+1);
		}
	}
	cout << ans << endl;
}

int main(void)
{
	solve();
	//cout << "yui(*-v・)yui" << endl;
	return 0;
}