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

int MAIN()
{
	double a, b, c, d;
	cin >> a >> b >> c >> d;
	c = min(c, d / b * a);
	d = min(d, c / a * b);
	c = min(c, d / b * a);
	d = min(d, c / a * b);
	cout << (c + d) << endl;
	return 0;
}

int main()
{
	int start = clock();
	#ifdef LOCAL_TEST
		freopen("in.txt", "r", stdin);
		freopen("out.txt", "w", stdout);
	#endif
	ios :: sync_with_stdio(false);
	cout << fixed << setprecision(16);
	int ret = MAIN();
	#ifdef LOCAL_TEST
		cout << "[Finished in " << clock() - start << " ms]" << endl;
	#endif
	return ret;
}