#include <bits/stdc++.h>

using namespace std;

int main() {
  int P = 0, LP, WP;
  double G, L;

  cin >> LP >> WP >> G >> L;

  G *= 0.01;
  L *= 0.01;

  // em[p]: expected number of matches until a prize is received
  // if we start at probability p
  double em[101];

  // em[100] = 1 + lose*em[100] + win*0 ==> em[100] = 1/win
  em[100] = 1/(1-L);
  for (int i = 99; i >= 0; --i) {
    // play a game:
    //   - if we lose then no prize but go up by LP
    //   - if we win but fail to get a prize, go up by WP
    // em[i] = 1 + lose*em[i+LP] + win*noprize*em[i+WP]
    em[i] = 1 + L*em[min(i+LP, 100)] + (1-L)*(1-i*0.01)*em[min(i+WP, 100)];
  }

  // we play em[P] games to open the first prize pack
  // if it is not the gorilla suit, then every other attempt takes em[0] games
  double ans = em[0]/G;

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

  return 0;
}