#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

int main() {
    int32_t a, b, x, y;
    cin >> a >> b >> x >> y;
    double ans;
    if (a * y == b * x)
        ans = x + y;
    else if (a * y < b * x)
        ans = y + double(a * y) / b;
    else
        ans = x + double(b * x) / a;
    printf("%.9f\n", ans);
    return 0;
}