fabbbhgedd
 abbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaababbbaab
 hcdhgcchbdhbeagdcfedgcbaffebgcbcccadeefacbhefgeadfgchabgeebegahfgegahbddedfhffeadcedadgfbeebhgfahhfb
 khjcoijiicdkdianmdolmadobdkcmgifdnffddnjehhbldlkjffknficdcmokfacioiegjedbmadjioomdacbodcajcmonmnlabo
 bababbdaee
 cbbbbcaaca
 gaejllebhn
 eaaebccaeacdecaedcaabbbdeebccdcdaabeeaeeaddbaabdccebecebbbbedbdcbbbbbbecbaddcddcccdcbbadbecddecedbba
 difhjdjbcdjedhiegagdejkbjfcdcdagdijdjajecbheiabfbjdgjdecfhdkgdbkcgcgakkiiggfkgcfadkjhiijkjacgejfhjge
 bbababaaababaabbbbbabbbbbbaaabbabaaaaabbbbbaaaabbbbabaabaabababbbabbabbabaaababbabbababaaaaabaaaabbb
 cadbcdddda
 kpsaloedscghjeaqadfhmlibjepjafdomkkorinrpakondtnrnknbqarbejcenrlsbfgdbsdmkpphbkdnbitjfcofsjibssmmlll
 aaabbbaaaabbbbaaabbbbbaabbbbaaababbaaabbbbaaabbbbababbbbaaabbbbaaabbbbbaabbbbaaabbbbaaabbbb
 ibledofnibedebifmnjdoaijeghajecbkjaebbkofnacceaodiifbhgkihkibddneeiemacodeafeaiiiaoajhmkjffbmmiehebhokfklhbkeoanoajdedjdlkbhenidclagggfhhhldfleccgmjbkhaginlhabkabagikalccndciokabfaebjkndf
 abbacba
 jkeaagakbifeaechkifkdghcjcgighidcgdccfbdbcackfgaebkddabgijkhjkaffkabacekdkjekeccegbecbkecbgbgcacgdackcdfjefaifgbigahkbedidfhjbikejdhejcgideaeejdcegeeccaefbddejkbdkfagfcdjbikbidfggkidcdcic

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

#include<bits/stdc++.h>
using namespace std;

#define ll long long
#define ld long double
#define pii pair<int, int>
#define pll pair<ll, ll>
#define vi vector<int>
#define vll vector<ll>
#define vpii vector<pair<int,int>>
#define vpll vector<pair<ll,ll>>
#define fr(i,k,n) for (int i = k; i < n; ++i)
#define fri(i,k,n) for (int i = k; i >= n; --i)
#define INF (int)1e9
#define MOD 1000000007
#define pb push_back
#define mp make_pair
#define all(arr) arr.begin(),arr.end()

void boost(){
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
}

void solve(){
	string s;
	cin>>s;
	int l=s.size();
	s=s+s;
	ll cnt1=0;
	vi start[26];
	fr(i,0,l){
		start[s[i]-'a'].pb(i);
	}
	int cnt[26]={0};
	int mark[l+1]={0};
	int from[26]={0};
	fr(i,0,26){
		fr(j,1,l){
			memset(cnt,0,sizeof(cnt));
			memset(from,0,sizeof(from));
			for(auto x: start[i]){
				if(mark[x]==1)
					continue;
				from[s[x+j]-'a']=x;
				cnt[s[x+j]-'a']++;
			}
			fr(k,0,26){
				if(cnt[k]==1){
					mark[from[k]]=1;
					cnt1++;
				}
			}
		}
	}
	ld num=cnt1;
	ld den=l;
	cout<<fixed<<setprecision(12)<<(num/den)<<endl;
	return;
}

int main()
{
	boost();
	
	int tc=1;
	//cin>>tc;
	while(tc--)
		solve();
	return 0;
}