#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <cctype>
using namespace std;
typedef long long ll;

int main()
{
	double a, b, x, y;
	cin >> a >> b >> x >> y;
	if (a >= b)
	{
		b /= a;
		cout << fixed << setprecision(10) << x*(1 + b) << endl;
	}
	else
	{
		a /= b;
		cout << fixed << setprecision(10) << y*(a + 1) << endl;
	}
	return 0;
}