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1.000000000000000
 0.000000000000000
 0.450000000000000
 0.960000000000000
 1.000000000000000
 0.800000000000000
 1.000000000000000
 0.080000000000000
 0.840000000000000
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#include <bits/stdc++.h>
using namespace std;
int check(vector<int> a, string s) {
  map<char, vector<int>> c;
  unordered_set<int> answer;
  int n = s.size();
  for (int i = 1; i < n; i++) {
    for (int j : a) c[s[(j + i) % n]].push_back(j);
    for (auto k = c.begin(); k != c.end(); k++)
      if (k->second.size() == 1) answer.insert(k->first);
    c.clear();
  }
  return answer.size();
}
int main() {
  map<char, vector<int>> a;
  string s;
  int i, d = 0;
  getline(cin, s);
  for (i = 0; i < s.size(); i++) a[s[i]].push_back(i);
  for (pair<char, vector<int>> j : a) {
    if (j.second.size() == 1) {
      cout << '1';
      return 0;
    }
    d += check(j.second, s);
  }
  cout << (double)d / s.size();
  return 0;
}
