#include <bits/stdc++.h>
using namespace std;
const long long int mod = 1000000007;
const long long int inf = 0x3f3f3f3f3f3f3f3fLL;
const double eps = 1e-9;
const double PI = acos(-1);
long long int i, j, k;
void solve(void);
inline bool equal(double a, double b) { return fabs(a - b) < eps; }
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(10);
  int t = 1;
  while (t--) solve();
  return 0;
}
void solve() {
  string s;
  cin >> s;
  int n = (long long)s.size();
  unordered_map<char, vector<int> > v;
  for (i = (0); i <= (n - 1); ++i) v[s[i]].emplace_back(i);
  string t[n];
  for (i = (0); i <= (n - 1); ++i) {
    string temp;
    for (j = (i); j <= (n - 1); ++j) temp += s[j];
    for (j = (0); j <= (i - 1); ++j) temp += s[j];
    t[i] = temp;
  }
  int cnt = 0;
  for (auto it : v) {
    long long int ct = 0;
    for (i = (1); i <= (n - 1); ++i) {
      int hash[26] = {0};
      for (auto jt : it.second) hash[t[jt][i] - 'a']++;
      long long int x = 0;
      for (j = (0); j <= (25); ++j)
        if (hash[j] == 1) ++x;
      ct = ((ct) > (x) ? (ct) : (x));
    }
    cnt += ct;
  }
  cout << cnt / double(n) << '\n';
}
