#include <iostream>
#include <iomanip>
#include <cstdio>
#include <vector>
#include <queue>

#include <map>
#include <set>
#include <string>
#include <algorithm>
#include <functional>
using namespace std;
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define INF 1<<30
#define MP make_pair
#define mp make_pair
#define pb push_back
#define PB push_back
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define ll long long
#define ull unsigned long long

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  double a, b, x, y;
  cin >> a >> b >> x >> y;

  double res = 0.0;
  if(x * b >= y * a) {
    res = y + y * a / b;
  } else {
    res = x + x * b / a;
  }

  cout <<  setprecision(20) << res << endl;
}