Problem: Vasya and Kolya play a game with a string, using the following rules. Initially, Kolya creates a string s, consisting of small English letters, and uniformly at random chooses an integer k from a segment [0, len(s) - 1]. He tells Vasya this string s, and then shifts it k letters to the left, i. e. creates a new string t = sk + 1sk + 2... sns1s2... sk. Vasya does not know the integer k nor the string t, but he wants to guess the integer k. To do this, he asks Kolya to tell him the first letter of the new string, and then, after he sees it, open one more letter on some position, which Vasya can choose.

Vasya understands, that he can't guarantee that he will win, but he wants to know the probability of winning, if he plays optimally. He wants you to compute this probability. 

Note that Vasya wants to know the value of k uniquely, it means, that if there are at least two cyclic shifts of s that fit the information Vasya knowns, Vasya loses. Of course, at any moment of the game Vasya wants to maximize the probability of his win.

Input

The only string contains the string s of length l (3 ≤ l ≤ 5000), consisting of small English letters only.

Output

Print the only number — the answer for the problem. You answer is considered correct, if its absolute or relative error does not exceed 10 - 6.

Formally, let your answer be a, and the jury's answer be b. Your answer is considered correct if <image>

Examples

Input

technocup


Output

1.000000000000000


Input

tictictactac


Output

0.333333333333333


Input

bbaabaabbb


Output

0.100000000000000

Note

In the first example Vasya can always open the second letter after opening the first letter, and the cyclic shift is always determined uniquely.

In the second example if the first opened letter of t is "t" or "c", then Vasya can't guess the shift by opening only one other letter. On the other hand, if the first letter is "i" or "a", then he can open the fourth letter and determine the shift uniquely.

Solution (in JAVA):

Solution:

import java.io.*;
import java.util.*;
import java.util.function.IntUnaryOperator;


/**
 * gl hf
 */
public class Main {
    static class MyRunnable implements Runnable {
        @Override
        public void run() {

        }

        public void start() {

        }
    }
    static class Task {
        PrintWriter out;
        String s;
        int n;
        public void solve(MyScanner in, PrintWriter out) {
            this.out = out;

            s = in.nextLine();
              n = s.length();

            double res = 0;

             for (char x = 'a'; x <= 'z'; x++) {
                 List<Integer> startIndex = new ArrayList<>();
                 for (int i = 0; i < n; i++) {
                     if (s.charAt(i) == x) {
                         startIndex.add(i);
                     }
                 }

                 double probChar = ((double) startIndex.size()) / n;

                 if (startIndex.size() > 0) {

                     double maxProb = 0;
                     for (int i = 1; i < n; i++) { // ????
                         maxProb = Math.max(maxProb, getProb(x, i, startIndex));
                     }

                    // out.println("Cahr " + x + " max prob " + maxProb);
                     res += maxProb * probChar;
                 }
             }



             out.println(res);
        }

        private double getProb(char c, int offset, List<Integer> startIndex ) {
            if (startIndex.size() == 0) return  0;

            Map<Character, Integer> map = new HashMap<>();

            for (Integer x: startIndex) {
                int ind = (x + offset) % n;
                char charAt = s.charAt(ind);
                int ct = map.getOrDefault(charAt, 0);
                map.put(charAt, ct + 1);
            }

            int uniq = 0;
            int sum = 0;
            for (Integer v: map.values()) {
                if (v == 1) {
                    uniq+=v;
                }
                sum += v;
            }
            //if (uniq > 0)  out.println("uniq " + uniq + " when " + c + " " +offset + " " + (uniq / sum));

            return ((double) uniq )/ sum;
        }

        private boolean can(List<Integer> startIndex) {
            if (startIndex.size() == 0) return false;

            HashSet<Character> currentChars = new HashSet<>();

            for (int offset = 1; offset < n; offset++) {
                currentChars.clear();
                boolean wasSame = false;
                for (Integer i : startIndex) {
                    char willAdd = s.charAt((i + offset) % n);
                    if (currentChars.contains(willAdd)) {
                        wasSame = true;
                        break;
                    } else {
                        currentChars.add(willAdd);
                    }
                }

                if (!wasSame) {
                    out.println("Start ind " + startIndex + " w offset " + offset + " good");
                    return true;
                }

            }

            return false;
        }

        private void printArray(int[] arr) {
            //out.println("Printing arrray of size " + arr.length);
            for (int i = 0; i < arr.length; i++) {
                out.println("Arr[" + i + "] = " + arr[i]);
            }

        }

    }

    public static void main(String[] args) {
        MyScanner in = new MyScanner();
        PrintWriter out = new PrintWriter(System.out);
        Task solver = new Task();
        solver.solve(in, out);
        out.close();
    }

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            br = new BufferedReader(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 nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}