fabbbhgedd
 abbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaab
 hcdhgcchbdhbeagdcfedgcbaffebgcbcccadeefacbhefgeadfgchabgeebegahfgegahbddedfhffeadcedadgfbeebhgfahhfb
 khjcoijiicdkdianmdolmadobdkcmgifdnffddnjehhbldlkjffknficdcmokfacioiegjedbmadjioomdacbodcajcmonmnlabo
 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;
int used[26][26];
int main() {
  string s;
  int n;
  double ans = 0;
  int i, j, k;
  cin >> s;
  n = int(s.length());
  for (i = 1; i <= n; i++) {
    int cnt = 0;
    for (j = 0; j < 26; j++)
      for (k = 0; k < 26; k++) used[j][k] = 0;
    for (j = 0; j < n; j++) used[s[j] - 'a'][s[(j + i) % n] - 'a']++;
    for (j = 0; j < n; j++)
      if (used[s[j] - 'a'][s[(j + i) % n] - 'a'] < 2) cnt++;
    ans = max(ans, double(cnt) / double(n));
  }
  cout << fixed;
  cout.precision(10);
  cout << ans << endl;
  return 0;
}
