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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

/**
 * @author Don Li
 */
public class GameWithString {
    void solve() {
        char[] s = in.nextToken().toCharArray();
        int n = s.length;
        
        int[] cnt = new int[26];
        for (int i = 0; i < n; i++) cnt[s[i] - 'a']++;
        int[][] pos = new int[26][];
        for (int i = 0; i < 26; i++) pos[i] = new int[cnt[i]];
        for (int i = n - 1; i >= 0; i--) pos[s[i] - 'a'][--cnt[s[i] - 'a']] = i;
        
        s = Arrays.copyOf(s, n << 1);
        for (int i = 0; i < n; i++) s[n + i] = s[i];
        
        int ans = 0;
        for (int c = 0; c < 26; c++) {
            if (pos[c].length == 0) continue;
            int best = 0;
            for (int d = 1; d < n; d++) {
                int[] test = new int[26];
                for (int i : pos[c]) {
                    test[s[i + d] - 'a']++;
                }
                int distinct = 0;
                for (int i = 0; i < 26; i++) {
                    if (test[i] == 1) distinct++;
                }
                best = Math.max(best, distinct);
            }
            ans += best;
        }
        out.println((double) ans / n);
    }
    
    public static void main(String[] args) {
        in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)));
        out = new PrintWriter(System.out);
        new GameWithString().solve();
        out.close();
    }
    
    static FastScanner in;
    static PrintWriter out;
    
    static class FastScanner {
        BufferedReader in;
        StringTokenizer st;
        
        public FastScanner(BufferedReader in) {
            this.in = in;
        }
        
        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(in.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }
        
        public int nextInt() {
            return Integer.parseInt(nextToken());
        }
        
        public long nextLong() {
            return Long.parseLong(nextToken());
        }
        
        public double nextDouble() {
            return Double.parseDouble(nextToken());
        }
    }
}
