#include <bits/stdc++.h>
using namespace std;
const int base = 1000 * 1000 * 1000;
const int days[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int inf = (int)1e9;
const int mod = inf + 7;
vector<string> v[26];
bool b[5555];
int main() {
  string s;
  cin >> s;
  double cnt = 0;
  for (long long i = 0; i < s.size(); i++) {
    v[s[0] - 'a'].push_back(s);
    string y;
    for (long long i = 1; i < s.size(); i++) y += s[i];
    y += s[0];
    s = y;
  }
  for (long long i = 0; i < 26; i++) {
    vector<vector<int> > y(s.size(), vector<int>(26));
    vector<int> g(s.size(), 0);
    for (long long j = 0; j < v[i].size(); j++)
      for (int k = 1; k < v[i][j].size(); k++) y[k][v[i][j][k] - 'a']++;
    for (long long j = 0; j < v[i].size(); j++) {
      for (int k = 1; k < v[i][j].size(); k++)
        if (y[k][v[i][j][k] - 'a'] == 1) {
          g[k]++;
        }
    }
    double maxx = 0;
    for (long long j = 0; j < s.size(); j++) maxx = max(maxx, (double)g[j]);
    cnt += maxx;
  }
  printf("%.15f", cnt / s.size());
  return 0;
}
