#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int N, M;
  cin >> N >> M;
  vector<int> ceff(N * 2);
  for (int i = 0; i < N; ++i) {
    cin >> ceff[i * 2];
  }
  cin >> ceff[N * 2 - 1];
  for (int i = 1; i < N; ++i) {
    cin >> ceff[i * 2 - 1];
  }
  double cur = M;
  for (int i = N * 2 - 1; i >= 0; --i) {
    if (ceff[i] == 1) {
      cout << -1 << endl;
      return 0;
    }
    cur = cur / (ceff[i] - 1) + cur;
  }
  cout << setprecision(10) << fixed;
  cout << cur - M << endl;
  return 0;
}
