fabbbhgedd
 abbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaab
 hcdhgcchbdhbeagdcfedgcbaffebgcbcccadeefacbhefgeadfgchabgeebegahfgegahbddedfhffeadcedadgfbeebhgfahhfb
 khjcoijiicdkdianmdolmadobdkcmgifdnffddnjehhbldlkjffknficdcmokfacioiegjedbmadjioomdacbodcajcmonmnlabo
 bababbdaee
 cbbbbcaaca
 gaejllebhn
 eaaebccaeacdecaedcaabbbdeebccdcdaabeeaeeaddbaabdccebecebbbbedbdcbbbbbbecbaddcddcccdcbbadbecddecedbba
 difhjdjbcdjedhiegagdejkbjfcdcdagdijdjajecbheiabfbjdgjdecfhdkgdbkcgcgakkiiggfkgcfadkjhiijkjacgejfhjge
 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

import java.io.*;
import java.util.*;
import static java.lang.Math.*;

public class E {
    public static void main(String[] args) {
        Scanner input = new Scanner();
        StringBuilder output = new StringBuilder();

        String s = input.next();
        int n = s.length();
        int[][][] seen = new int[26][n][26];
        int[][] ones = new int[26][n];

        for (int i = 0; i < n; i++) {
            int first = s.charAt(i) - 'a';
            for (int j = 1; j < n; j++) {
                int second = s.charAt((i + j) % n) - 'a';
                seen[first][j][second]++;
                if (seen[first][j][second] == 1) {
                    ones[first][j]++;
                } else if (seen[first][j][second] == 2) {
                    ones[first][j]--;
                }
            }
        }
        double prob = 0;
        for (int i = 0; i < 26; i++) {
            int total = 0;
            for (int j = 0; j < n; j++) {
                total = max(total, ones[i][j]);
            }
            prob += (double)(total) / (double)n;
        }
        System.out.println(prob);
    }

    private static class Scanner {
        BufferedReader br; StringTokenizer st;
        public Scanner(Reader in) { br = new BufferedReader(in); }
        public Scanner() { this(new InputStreamReader(System.in)); }
        String next() {
            while (st == null || !st.hasMoreElements()) {
                try { st = new StringTokenizer(br.readLine());
                } catch (IOException e) { e.printStackTrace(); } }
            return st.nextToken(); }
        int nextInt() { return Integer.parseInt(next()); }
        long nextLong() { return Long.parseLong(next()); }
        double nextDouble() { return Double.parseDouble(next()); }
        String readNextLine() {
            String str = "";
            try { str = br.readLine();
            } catch (IOException e) { e.printStackTrace(); }
            return str; }
        int[] readIntArray(int n) {
            int[] a = new int[n];
            for (int idx = 0; idx < n; idx++) { a[idx] = nextInt(); }
            return a; }
        long[] readLongArray(int n) {
            long[] a = new long[n];
            for (int idx = 0; idx < n; idx++) { a[idx] = nextLong(); }
            return a; }
    } // end Scanner
}
