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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        char[] inputs = sc.next().toCharArray();
        List<TreeSet<Integer>> positions = new ArrayList<>();
        for (int i = 0; i < 26; i++) {
            positions.add(new TreeSet<>());
            positions.get(i).add(-1);
            positions.get(i).add(inputs.length);
        }
        long ans = (inputs.length + 1L) * inputs.length / 2 * 26;
        double base = (inputs.length + 1L) * inputs.length / 2;
        for (int i = 0; i < inputs.length; i++) {
            positions.get(inputs[i] - 'a').add(i);
        }
        for (TreeSet<Integer> current : positions) {
            Integer key = current.first();
            while ((key = current.higher(key)) != null) {
                int size = key - current.lower(key) - 1;
                ans -= (size + 1L) * size / 2;
            }
        }
        System.out.println(ans / base);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}