#include <bits/stdc++.h>
using namespace std;
char sir[10005];
int frecv[30][5005][30], n, nrpozd[5005];
long double prob;
vector<int> poz[30];
int main() {
  int i, j, maxi;
  cin >> sir;
  n = strlen(sir);
  for (i = n; i <= 2 * n - 1; i++) sir[i] = sir[i - n];
  sir[2 * n] = 0;
  for (i = 0; i < n; i++) {
    for (j = i; j <= i + n - 1; j++) frecv[sir[i] - 'a'][j - i][sir[j] - 'a']++;
    poz[sir[i] - 'a'].push_back(i);
  }
  for (i = 0; i <= 25; i++) {
    for (j = 1; j < n; j++) nrpozd[j] = 0;
    maxi = 0;
    for (j = 1; j < n; j++) {
      for (auto it = poz[i].begin(); it != poz[i].end(); ++it)
        if (frecv[i][j][sir[j + (*it)] - 'a'] == 1) nrpozd[j]++;
      maxi = max(maxi, nrpozd[j]);
    }
    prob += maxi;
  }
  prob /= n;
  cout << fixed << setprecision(10) << prob;
  return 0;
}
