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#include <bits/stdc++.h>
using namespace std;
const long long maxn = 2e6 + 6;
const long long MOD = 1e9 + 7;
bool comparator(long long i, long long j) { return (i < j); }
long long power(long long x, long long i) {
  long long ans = 1;
  while (i > 0) {
    if (i & 1) ans = (ans * x) % MOD;
    i >>= 1;
    x = (x * x) % MOD;
  }
  return ans;
}
long long power(long long x, long long i, long long mod) {
  long long ans = 1;
  while (i > 0) {
    if (i & 1) ans = (ans * x) % mod;
    i >>= 1;
    x = (x * x) % mod;
  }
  return ans;
}
long long modInverse(long long x, long long mod) {
  return power(x, mod - 2, mod);
}
bool isPalindrome(string s) {
  long long limit = s.length() / 2;
  for (long long i = 0; i < limit; i++) {
    if (s[i] != s[s.length() - i - 1]) return 0;
  }
  return true;
}
long long gcd(long long x, long long y) {
  long long t;
  while (y != 0) {
    t = x % y;
    x = y;
    y = t;
  }
  return x;
}
bool isVowel(char ch) {
  if (ch == 'a' || ch == 'i' || ch == 'e' || ch == 'u' || ch == 'o' ||
      ch == 'y') {
    return true;
  }
  return false;
}
bool isPrime(long long n) {
  long long root = sqrt(n);
  for (long long i = 2; i <= root; i++)
    if (n % i == 0) return 0;
  return 1;
}
long double getDis(long double asdfg, long double qwert, long double gfdsa,
                   long double trewq) {
  return sqrt((asdfg - gfdsa) * (asdfg - gfdsa) +
              (qwert - trewq) * (qwert - trewq));
}
long double getDisSquare(long double asdfg, long double qwert,
                         long double gfdsa, long double trewq) {
  return (asdfg - gfdsa) * (asdfg - gfdsa) + (qwert - trewq) * (qwert - trewq);
}
bool isSquareHelper(long long asdfg, long long qwert, long long gfdsa,
                    long long trewq, long long x3, long long y3, long long x4,
                    long long y4) {
  long double d1, d2, d3, d4, d5, d6;
  d1 = getDisSquare(asdfg, qwert, gfdsa, trewq);
  d2 = getDisSquare(gfdsa, trewq, x3, y3);
  d3 = getDisSquare(x3, y3, x4, y4);
  d4 = getDisSquare(x4, y4, asdfg, qwert);
  if (d1 == d2 && d1 == d3 && d1 == d4) {
    d5 = getDisSquare(asdfg, qwert, x3, y3);
    d6 = getDisSquare(gfdsa, trewq, x4, y4);
    if (d5 == d6) {
      return 1;
    }
  }
  return 0;
}
bool isSquare(long long asdfg, long long qwert, long long gfdsa,
              long long trewq, long long x3, long long y3, long long x4,
              long long y4) {
  if (isSquareHelper(asdfg, qwert, gfdsa, trewq, x3, y3, x4, y4) ||
      isSquareHelper(asdfg, qwert, gfdsa, trewq, x4, y4, x3, y3) ||
      isSquareHelper(asdfg, qwert, x3, y3, gfdsa, trewq, x4, y4))
    return 1;
  else
    return 0;
}
bool isEqualateralTriangle(long long asdfg, long long qwert, long long gfdsa,
                           long long trewq, long long x3, long long y3) {
  long long d1 = getDisSquare(asdfg, qwert, gfdsa, trewq);
  long long d2 = getDisSquare(gfdsa, trewq, x3, y3);
  long long d3 = getDisSquare(x3, y3, asdfg, qwert);
  if (d1 == d2 && d1 == d3) {
    return 1;
  } else
    return 0;
}
bool isRightAngleTriangleHelper(long long asdfg, long long qwert,
                                long long gfdsa, long long trewq, long long x3,
                                long long y3) {
  long long d1 = getDisSquare(asdfg, qwert, gfdsa, trewq);
  long long d2 = getDisSquare(gfdsa, trewq, x3, y3);
  long long d3 = getDisSquare(x3, y3, asdfg, qwert);
  if (d2 == (d1 + d3)) {
    return 1;
  }
  return 0;
}
bool isRightAngleTriangle(long long asdfg, long long qwert, long long gfdsa,
                          long long trewq, long long x3, long long y3) {
  if (isRightAngleTriangleHelper(asdfg, qwert, gfdsa, trewq, x3, y3) ||
      isRightAngleTriangleHelper(gfdsa, trewq, x3, y3, asdfg, qwert) ||
      isRightAngleTriangleHelper(x3, y3, asdfg, qwert, gfdsa, trewq))
    return 1;
  return 0;
}
bool areCollinear(long long asdfg, long long qwert, long long gfdsa,
                  long long trewq, long long x3, long long y3) {}
string s;
long long n, b[30], dp[30];
vector<long long> g[100];
void getInput() {
  cin >> s;
  n = s.length();
}
void solve() {
  for (long long i = 0; i < n; i++) {
    g[s[i] - 'a'].push_back(i);
  }
  for (long long i = 0; i < 26; i++) {
    if (g[i].size() == 0) continue;
    long long mx = 0, cnt;
    for (long long j = 1; j <= n - 1; j++) {
      for (long long i = 0; i < 26; i++) b[i] = 0;
      for (auto k : g[i]) {
        b[s[(k + j) % n] - 'a']++;
      }
      cnt = 0;
      for (long long k = 0; k < 26; k++) {
        if (b[k] == 1) cnt++;
      }
      mx = max(cnt, mx);
    }
    dp[i] = mx;
  }
  long double ans = 0;
  for (long long i = 0; i < 26; i++) {
    ans += dp[i];
  }
  cout << fixed << setprecision(10) << (long double)ans / (long double)n
       << "\n";
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  while (t--) getInput(), solve();
  return 0;
}
