#include <bits/stdc++.h>
using namespace std;
long long gcd(int a, int b) {
  while (a && b)
    if (a > b)
      a %= b;
    else
      b %= a;
  return a + b;
}
long long n;
long long m[20], r[20];
long long nok = 1;
long long *a;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> m[i];
    nok = nok * m[i] / gcd(nok, m[i]);
  }
  for (int i = 0; i < n; ++i) cin >> r[i];
  a = new long long[nok];
  for (int i = 0; i < nok; ++i) a[i] = 0;
  for (int i = 0; i < n; ++i)
    for (int j = 0; j < nok; ++j)
      if (j % m[i] == r[i]) a[j] = 1;
  long long sum = 0;
  for (int i = 0; i < nok; ++i) sum += a[i];
  cout << 1. * sum / nok << endl;
}
