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 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;
const int letternum = 26;
const int maxn = 5005;
bool checked[maxn];
int main() {
  string s;
  cin >> s;
  int n = s.size();
  s = s + s;
  vector<vector<int> > cnt(letternum);
  for (int i = 0; i < n; i++) {
    cnt[s[i] - 'a'].push_back(i);
  }
  int ans = 0;
  for (int c = 0; c < letternum; c++) {
    int best = 0;
    for (int i = 1; i < n; i++) {
      vector<int> num(letternum, 0);
      for (auto k : cnt[c]) {
        num[s[i + k] - 'a']++;
      }
      int tmp = 0;
      for (int i = 0; i < letternum; i++) tmp += num[i] == 1;
      if (best < tmp) best = tmp;
    }
    ans += best;
  }
  printf("%.8lf\n", (double)ans / n);
  return 0;
}
