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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
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 0.786096256684492
 1.000000000000000
 0.438502673796791

#include <bits/stdc++.h>
using namespace std;
int a[800];
int b[26];
char s[5555];
int main() {
  cin >> s;
  int n = strlen(s);
  int ans = 0;
  memset(b, 0, sizeof(b));
  for (int i = 1; i <= n - 1; i++) {
    memset(a, 0, sizeof(a));
    for (int j = 0; j < n; j++) {
      int t = (j + i) % n;
      int x = ((s[j] - 'a') * 26 + (s[t] - 'a'));
      a[x]++;
    }
    for (int j = 0; j < 26; j++) {
      int cnt = 0;
      for (int k = 0; k < 26; k++) {
        if (a[j * 26 + k] == 1) cnt++;
      }
      b[j] = max(b[j], cnt);
    }
  }
  for (int i = 0; i < 26; i++) ans += b[i];
  double nee = (double)ans / (double)n;
  printf("%.10lf\n", nee);
  return 0;
}
