#include <bits/stdc++.h>

#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORTASC(c) sort((c).begin(),(c).end())
#define SORTDESC(c,t) sort((c).begin(),(c).end(), std::greater<t>());
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

const double PI  = acos(-1.0);

using ll = long long;
using namespace std;

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

    cin >> a >> b >> x >> y;
    
    if (x*(b/a) < y) {
        ans = x*(a+b)/a;
    } else {
        ans = y*(a+b)/b;
    }

    cout << setprecision(20) << ans << endl;

    return 0;
}