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 cadbcdddda
 kpsaloedscghjeaqadfhmlibjepjafdomkkorinrpakondtnrnknbqarbejcenrlsbfgdbsdmkpphbkdnbitjfcofsjibssmmlll
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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>
#pragma GCC optimize("O2")
using namespace std;
inline long long input() {
  long long n;
  cin >> n;
  return n;
}
const int MAXN = 5e3 + 10;
const int MOD = 1e9 + 7;
const int MOD2 = 998244353;
const long long INF = 8e18;
long long pw(long long a, long long b) {
  return (!b ? 1
             : (b & 1 ? (a * pw(a * a % MOD, b / 2)) % MOD
                      : pw(a * a % MOD, b / 2)));
}
long long cnt[30][MAXN][30];
long double P[MAXN];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  cout << fixed << setprecision(15);
  string s;
  cin >> s;
  int n = (int)s.size();
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      if (i == j) continue;
      cnt[s[i] - 'a'][(i - j + n) % n][s[j] - 'a']++;
    }
  }
  for (int i = 0; i < 26; i++) {
    for (int j = 1; j < n; j++) {
      int p = 0, q = 0;
      for (int k = 0; k < 26; k++) {
        q += cnt[i][j][k];
        if (cnt[i][j][k] == 1) p++;
      }
      long double BI = 1.0;
      P[i] = max(P[i], BI * p / q);
    }
  }
  long double ans = 0;
  for (int i = 0; i < n; i++) ans += (1.0 / n) * P[s[i] - 'a'];
  cout << ans;
  return 0;
}
