#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    double a, b, x, y;
    cin >> a >> b >> x >> y;

    double ans;
    if(x / a * b < y)
        ans = x + (x / a * b);
    else
        ans = y + (y / b * a);
    printf("%.10f\n", ans);

    return 0;
}