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 bababbdaee
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 gaejllebhn
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 bbababaaababaabbbbbabbbbbbaaabbabaaaaabbbbbaaaabbbbabaabaabababbbabbabbabaaababbabbababaaaaabaaaabbb
 cadbcdddda
 kpsaloedscghjeaqadfhmlibjepjafdomkkorinrpakondtnrnknbqarbejcenrlsbfgdbsdmkpphbkdnbitjfcofsjibssmmlll
 aaabbbaaaabbbbaaabbbbbaabbbbaaababbaaabbbbaaabbbbababbbbaaabbbbaaabbbbbaabbbbaaabbbbaaabbbb
 ibledofnibedebifmnjdoaijeghajecbkjaebbkofnacceaodiifbhgkihkibddneeiemacodeafeaiiiaoajhmkjffbmmiehebhokfklhbkeoanoajdedjdlkbhenidclagggfhhhldfleccgmjbkhaginlhabkabagikalccndciokabfaebjkndf
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1.000000000000000
 0.000000000000000
 0.450000000000000
 0.960000000000000
 1.000000000000000
 0.800000000000000
 1.000000000000000
 0.080000000000000
 0.840000000000000
 0.000000000000000
 0.800000000000000
 1.000000000000000
 0.000000000000000
 0.786096256684492
 1.000000000000000
 0.438502673796791

import java.io.*;
import java.util.*;
public class CF931_D2_E{
	public static void main(String[] args)throws Throwable {
		MyScanner sc=new MyScanner();
		PrintWriter pw=new PrintWriter(System.out);
		
		String s=sc.next();
		int n=s.length();
		ArrayList<String> [] arr=new ArrayList [26];
		for(int i=0;i<26;i++)
			arr[i]=new ArrayList<String>();
		for(int i=0;i<n;i++){
			s=s.substring(1)+s.charAt(0);
			arr[s.charAt(0)-'a'].add(s);
		}
		double ans=0;
		for(int i=0;i<26;i++){
			int mx=0;
			for(int j=1;j<n;j++){
				boolean [] v=new boolean [26];
				boolean [] valid=new boolean [26];
				Arrays.fill(valid, true);
				for(int k=0;k<arr[i].size();k++){
					if(v[arr[i].get(k).charAt(j)-'a'])
						valid[arr[i].get(k).charAt(j)-'a']=false;
					v[arr[i].get(k).charAt(j)-'a']=true;
				}
				int cc=0;
				for(int ii=0;ii<26;ii++)
					if(v[ii] && valid[ii])
						cc++;
				mx=Math.max(mx, cc);
			}
			ans+=(1.0*mx/n);
		}
		pw.println(ans);
		pw.flush();
		pw.close();
	}
	
	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;}
	}
} 