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 bbababaaababaabbbbbabbbbbbaaabbabaaaaabbbbbaaaabbbbabaabaabababbbabbabbabaaababbabbababaaaaabaaaabbb
 cadbcdddda
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1.000000000000000
 0.000000000000000
 0.450000000000000
 0.960000000000000
 1.000000000000000
 0.800000000000000
 1.000000000000000
 0.080000000000000
 0.840000000000000
 0.000000000000000
 0.800000000000000
 1.000000000000000
 0.000000000000000
 0.786096256684492
 1.000000000000000
 0.438502673796791

#include <bits/stdc++.h>
using namespace std;
void solve() {
  string s;
  cin >> s;
  long long int n = long long int(s.length()), tot = 0;
  vector<vector<string>> v(26);
  vector<long long int> res(n, 0);
  for (long long int i = 0; i < n; i++)
    v[long long int(s[i] - 'a')].push_back(s.substr(i, n - i) + s.substr(0, i));
  for (long long int c = 0; c < 26; c++)
    for (long long int i = 0; i < n; i++) {
      vector<long long int> vis(26);
      for (long long int j = 0; j < v[c].size(); j++) {
        long long int x = long long int(v[c][j][i] - 'a');
        vis[x]++;
      }
      for (long long int j = 0; j < 26; j++)
        if (vis[j] == 1) res[i]++;
    }
  long long int hi = 0;
  for (long long int i = 0; i < n; i++) hi = max(hi, res[i]);
  cout << fixed << setprecision(100) << (1.0 * hi / n);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t = 1;
  for (long long int i = 0; i < t; i++) solve();
}
