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 bababbdaee
 cbbbbcaaca
 gaejllebhn
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 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;
signed main() {
  string s;
  cin >> s;
  long long N = s.size();
  vector<long long> pos[26];
  long long sz[26] = {0};
  for (long long i = 0; i < (N); i++) {
    pos[s[i] - 'a'].push_back(i);
    sz[s[i] - 'a']++;
  }
  s += s;
  double ans = 0;
  for (long long i = 0; i < (26); i++) {
    long long maxVal = 0;
    for (long long j = 1; j <= N - 1; j++) {
      long long cnt[26] = {0};
      for (long long k = 0; k < (sz[i]); k++) {
        cnt[s[pos[i][k] + j] - 'a']++;
      }
      long long unique_count = 0;
      for (long long k = 0; k < (26); k++) {
        if (cnt[k] == 1) unique_count++;
      }
      maxVal = max(maxVal, unique_count);
    }
    ans += (double)maxVal / N;
  }
  printf("%.20lf\n", ans);
}
