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1.000000000000000
 0.000000000000000
 0.450000000000000
 0.960000000000000
 1.000000000000000
 0.800000000000000
 1.000000000000000
 0.080000000000000
 0.840000000000000
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 0.786096256684492
 1.000000000000000
 0.438502673796791

#include <bits/stdc++.h>
using namespace std;
const int OO = 1e9;
const long long INF = 1e18;
const int irand(int lo, int hi) {
  return ((double)rand() / (RAND_MAX + 1.0)) * (hi - lo + 1) + lo;
}
const long long lrand(long long lo, long long hi) {
  return ((double)rand() / (RAND_MAX + 1.0)) * (hi - lo + 1) + lo;
}
template <typename T>
T getnum() {
  int sign = 1;
  T ret = 0;
  char c;
  do {
    c = getchar();
  } while (c == ' ' || c == '\n');
  if (c == '-')
    sign = -1;
  else
    ret = c - '0';
  while (1) {
    c = getchar();
    if (c < '0' || c > '9') break;
    ret = 10 * ret + c - '0';
  }
  return sign * ret;
}
inline void ini(int& x) { x = getnum<int>(); }
inline void scani(int& x) { scanf("%d", &x); }
const int N = 5005;
int n;
string str;
vector<int> pos[28];
double ans[28];
int vis[28];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> str;
  n = str.size();
  for (int i = 0; i < n; i++) {
    pos[str[i] - 'a'].push_back(i);
  }
  for (int c = 0; c < 26; c++) {
    for (int i = 1; i <= n - 1; i += 1) {
      for (int k = 0; k < 26; k++) vis[k] = 0;
      for (int j = 0; j < pos[c].size(); j++) {
        char x = str[(pos[c][j] + i) % n];
        vis[x - 'a']++;
      }
      double tmp = 0;
      for (int k = 0; k < 26; k++) {
        if (vis[k] == 1) {
          tmp += (double)1 / n;
        }
      }
      ans[c] = max(ans[c], tmp);
    }
  }
  double anss = 0;
  for (int c = 0; c < 26; c++) {
    anss += ans[c];
  }
  cout << fixed << setprecision(12) << anss << endl;
  return 0;
}
