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import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.io.Writer;
import java.io.BufferedReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author palayutm
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        ProblemEGameWithString solver = new ProblemEGameWithString();
        solver.solve(1, in, out);
        out.close();
    }

    static class ProblemEGameWithString {
        public void solve(int testNumber, InputReader in, OutputWriter out) {
            String s = in.next();
            int n = s.length();
            ArrayList<Integer>[] arr = new ArrayList[26];
            for (int i = 0; i < 26; i++) {
                arr[i] = new ArrayList<>();
            }
            for (int i = 0; i < n; i++) {
                arr[s.charAt(i) - 'a'].add(i);
            }
            int ans = 0;
            for (int i = 0; i < 26; i++) {
                int mx = 0;
                for (int j = 0; j < n; j++) {
                    int[] cnt = new int[26];
                    for (int p : arr[i]) {
                        cnt[s.charAt((p + j) % n) - 'a']++;
                    }
                    int c = 0;
                    for (int k = 0; k < 26; k++) {
                        if (cnt[k] == 1) c++;
                    }
                    mx = Math.max(mx, c);
                }
                ans += mx;
            }
            out.printf("%.10f\n", 1.0 * ans / n);
        }

    }

    static class OutputWriter extends PrintWriter {
        public OutputWriter(OutputStream out) {
            super(out);
        }

        public OutputWriter(Writer out) {
            super(out);
        }

        public void close() {
            super.close();
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
}

