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1.000000000000000
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 0.450000000000000
 0.960000000000000
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 1.000000000000000
 0.080000000000000
 0.840000000000000
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#include <bits/stdc++.h>
using namespace std;
inline void Boost() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
}
int main() {
  Boost();
  string s;
  cin >> s;
  int n = (int)s.size();
  s = s + s;
  vector<vector<int> > G(26);
  for (int i = 0; i < n; ++i) {
    G[s[i] - 'a'].push_back(i);
  }
  long double let = n;
  long double goodLet = 0;
  for (auto it : G) {
    if (it.empty()) continue;
    for (int d = 1; d < n; ++d) {
      vector<bool> aux(26, false);
      bool ok = true;
      for (auto x : it) {
        int nxt = (s[x + d] - 'a');
        if (aux[nxt] == true) {
          ok = false;
          break;
        } else {
          aux[nxt] = true;
        }
      }
      if (ok) {
        goodLet += (int)it.size();
        break;
      }
    }
  }
  cout << fixed << setprecision(10) << goodLet / let;
  return 0;
}
