#include <bits/stdc++.h>
using namespace std;
template <class T>
void show(const vector<T> &a) {
  for (T x : a) cout << x << " ";
  cout << '\n';
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng_64(chrono::steady_clock::now().time_since_epoch().count());
vector<long long> xx = {1, 0, -1, 0};
vector<long long> yy = {0, 1, 0, -1};
string dir = "LRUD";
const long long N = 3e5 + 50, oo = 2e18 + 500;
const long long mod = 998244353;
const long long M2 = 1000000093, x2 = 27162;
const long long M1 = 1000000087, x1 = 241;
const double eps = 1e-12, PI = 2 * acos(0.0);
long long n, m, k;
long long cnt = 0;
long long lg = 18;
vector<vector<long long>> g;
vector<vector<long long>> rg;
signed main() {
  ios::sync_with_stdio(0);
  cout.tie(0);
  cin.tie(0);
  string s;
  cin >> s;
  n = ((long long)(s.size()));
  vector<vector<string>> vc(26);
  for (long long i = 0; i < n; i++) {
    string t = s.substr(i, n - i) + s.substr(0, i);
    vc[s[i] - 'a'].push_back(t);
  }
  double ans = 0;
  for (long long i = 0; i < 26; i++) {
    if (!((long long)(vc[i].size()))) continue;
    long long val = 0;
    for (long long j = 0; j < n; j++) {
      vector<long long> count_letters(26);
      for (long long z = 0; z < ((long long)(vc[i].size())); z++) {
        count_letters[vc[i][z][j] - 'a']++;
      }
      bool fl = 1;
      long long cur = 0;
      for (long long z = 0; z < 26; z++) {
        if (count_letters[z] == 1) {
          cur++;
        } else {
          if (count_letters[z]) fl = 0;
        }
      }
      if (fl) {
        val = ((long long)(vc[i].size()));
        break;
      }
      val = max(val, cur);
      ;
    }
    cnt += val;
  }
  ans = (double)cnt / (double)n;
  cout << fixed << setprecision(10) << ans;
}
