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 abbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaab
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 bababbdaee
 cbbbbcaaca
 gaejllebhn
 eaaebccaeacdecaedcaabbbdeebccdcdaabeeaeeaddbaabdccebecebbbbedbdcbbbbbbecbaddcddcccdcbbadbecddecedbba
 difhjdjbcdjedhiegagdejkbjfcdcdagdijdjajecbheiabfbjdgjdecfhdkgdbkcgcgakkiiggfkgcfadkjhiijkjacgejfhjge
 bbababaaababaabbbbbabbbbbbaaabbabaaaaabbbbbaaaabbbbabaabaabababbbabbabbabaaababbabbababaaaaabaaaabbb
 cadbcdddda
 kpsaloedscghjeaqadfhmlibjepjafdomkkorinrpakondtnrnknbqarbejcenrlsbfgdbsdmkpphbkdnbitjfcofsjibssmmlll
 aaabbbaaaabbbbaaabbbbbaabbbbaaababbaaabbbbaaabbbbababbbbaaabbbbaaabbbbbaabbbbaaabbbbaaabbbb
 ibledofnibedebifmnjdoaijeghajecbkjaebbkofnacceaodiifbhgkihkibddneeiemacodeafeaiiiaoajhmkjffbmmiehebhokfklhbkeoanoajdedjdlkbhenidclagggfhhhldfleccgmjbkhaginlhabkabagikalccndciokabfaebjkndf
 abbacba
 jkeaagakbifeaechkifkdghcjcgighidcgdccfbdbcackfgaebkddabgijkhjkaffkabacekdkjekeccegbecbkecbgbgcacgdackcdfjefaifgbigahkbedidfhjbikejdhejcgideaeejdcegeeccaefbddejkbdkfagfcdjbikbidfggkidcdcic

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 N = 5e3 + 10;
int vis[30], v[30];
;
vector<int> V[30];
int main() {
  string s;
  cin >> s;
  int n = s.length();
  for (int i = 0; i < s.length(); i++) {
    V[s[i] - 'a'].push_back(i);
  }
  for (int i = 0; i < 26; i++) {
    if (V[i].size()) {
      for (int j = 1; j < n; j++) {
        int f = 1;
        memset(v, 0, sizeof v);
        for (int x : V[i]) {
          int q = s[(x + j) % n] - 'a';
          if (v[q] == 1) {
            f = 0;
            break;
          }
          v[q]++;
        }
        vis[i] = f;
        if (f) break;
      }
    }
  }
  int cnt = 0;
  for (int i = 0; i < n; i++) {
    if (vis[s[i] - 'a']) {
      cnt++;
    }
  }
  if (!cnt) cnt = 1;
  printf("%.10f\n", cnt * 1.0 / n);
  return 0;
}
