#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, m, p = 0, q = 0, l = 0, i, flag = 0, k, t, j, r = 0, curr = 0, d;
  cin >> n >> m;
  long long a[n], b[n];
  long double q1 = 1.0000;
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    q1 *= double(a[i]) / double(a[i] - 1);
    if (a[i] == 1) {
      flag = 1;
    }
  }
  for (long long i = 0; i < n; i++) {
    cin >> b[i];
    q1 *= double(b[i]) / double(b[i] - 1);
    if (b[i] == 1) {
      flag = 1;
    }
  }
  if (flag == 1)
    cout << -1 << '\n';
  else {
    long double x = q1 * m - m;
    if (x < 0)
      cout << -1 << '\n';
    else
      cout << fixed << setprecision(10) << x << '\n';
  }
  return 0;
}
