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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
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import java.util.*;
import java.io.*;

import static java.lang.Math.*;

public class cfs468E {

    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        StringBuilder sb = new StringBuilder();
        char[] letters = sc.next().toCharArray();
        int n = letters.length;
        int[] allLetterFreq = new int[26];
        for (int i : letters) {
            allLetterFreq[i - 'a']++;
        }
        int[][][] freq = new int[26][26][n];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) { // j is the offset
                freq[letters[i] - 'a'][letters[((j+i)%n+n)%n] - 'a'][j]++;
            }
        }
        double sum = 0;
        for (int i = 0; i < 26; i++) { // given first letter is i
            // determine which offset j will give best information
            if (allLetterFreq[i] == 0) continue;

            int mostDistinct = 0;
            for (int j = 0; j < n; j++) {
                int distinct = 0;
                for (int k = 0; k < 26; k++) {
                    if (freq[i][k][j] == 1) distinct++;
                }
                mostDistinct = Math.max(mostDistinct, distinct);
            }
            double toAdd = (allLetterFreq[i] / (n * 1.0)) * ((1.0 * mostDistinct) / allLetterFreq[i]);
            sum += toAdd;
        }
        sb.append(sum);


        System.out.print(sb);
    }


    public static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner(Reader in) {
            br = new BufferedReader(in);
        }

        public FastScanner() {
            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;
        }
    }
}
