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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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 1.000000000000000
 0.438502673796791

#include <bits/stdc++.h>
using namespace std;
int main() {
  map<char, int> number;
  map<char, int>::iterator y;
  double q;
  map<double, int> map2;
  map<double, int>::iterator fin;
  long int a, b, c, d = 0, i, n, k = 3;
  map<pair<char, char>, long int> map1;
  map<pair<char, char>, long int>::iterator it;
  string wor, tor;
  cin >> wor;
  n = wor.length();
  tor = wor + wor;
  for (k = 1; k < n; k++) {
    d = 0;
    for (i = 0; i < n; i++) {
      map1[make_pair(tor[i], tor[i + k])] =
          map1[make_pair(tor[i], tor[i + k])] + 1;
    }
    for (it = map1.begin(); it != map1.end(); it++) {
      if (it->second == 1) {
        d = d + 1;
      }
    }
    map2.insert(make_pair(d, k));
    map1.clear();
  }
  fin = map2.end();
  fin--;
  cout.precision(15);
  cout << fixed << (double)fin->first / (double)n;
}
