//#pragma comment(linker,"/STACK:1024000000,1024000000")

#include<iostream>

#include<cstdio>

#include<string>

#include<cstring>

#include<vector>

#include<cmath>

#include<queue>

#include<stack>

#include<map>

#include<set>

#include<algorithm>

#include <stack>

#include <bitset>

#include <iomanip>

using namespace std;

const int SZ=,INF=0x7FFFFFFF;

typedef long long lon;

bool vst[];

set<int> st[];

short cnt[SZ][];

double work(int n,const string &str)

{

    int res=;

    for(int i=;i<;++i)

    {

        if(st[i].size()==)continue;

        memset(cnt,,sizeof(cnt));

        for(auto it=st[i].begin();it!=st[i].end();++it)

        {

            int pos=*it;

            for(int j=;j<n;++j)

            {

                ++cnt[j][str[(pos+j)%n]-'a'];

            }

        }

        int maxv=;

        for(int j=;j<n;++j)

        {

            maxv=max(maxv,(int)count(cnt[j],cnt[j]+,));

        }

        res+=maxv;

    }

    //cout<<res<<" "<<str.size()<<endl;

    return (double)res/str.size();

}

int main()

{

    std::ios::sync_with_stdio();

    //freopen("d:\\1.txt","r",stdin);

    //for(;scanf("%d",&n)!=EOF;)

    {

        string str;

        cin>>str;

        for(int i=;i<str.size();++i)

        {

            st[str[i]-'a'].insert(i);

        }

        cout<<fixed<<setprecision()<<work(str.size(),str)<<endl;

    }

    return ;

}