#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll,ll>
#define pii pair<int,int>
#define fs first
#define sc second
#define tlll tuple<ll,ll,ll>
const ll inf = 1e18;
const int mxg = 15;
const int mxn = 1e5+10;
ll prec[mxg][mxg][mxn];
int G,N;
string s;
vector<int> pos[mxg];
ll dp[1<<mxg];//ans * 4
void getprec(int a,int b){
if(a == b)return;
ll sum = 0;
int cnt = 0;
for(int i = 0;i<=N;i++){
if(s[i] == 'A'+a)sum += cnt;
else if(s[i] == 'A'+b)cnt++;
prec[a][b][i] += sum;
}
sum = 0;
cnt = 0;
for(int i = N;i>=0;i--){
prec[a][b][i] += sum;
if(s[i] == 'A'+a)sum += cnt;
else if(s[i] == 'A'+b)cnt++;
}
return;
}
ll f(ll from,ll cut,int add){
ll re = 0;
for(int i = 0;i<G;i++){
if(from&(1<<i))re += prec[add][i][cut]*4;
}
ll p = upper_bound(pos[add].begin(),pos[add].end(),cut)-pos[add].begin();
re += p*(p-1)+1ll*(pos[add].size()-p)*(int(pos[add].size())-p-1);
return re;
}
void trans(int from,int to,int add){
int l = 0,r = int(pos[add].size());
for(int i = 0;i<20&&l < r;i++){
int mid = (l+r)>>1;
int fl = (mid?f(from,pos[add][mid-1],add):f(from,0,add));
int fr = f(from,pos[add][mid],add);
if(fl<=fr)r = mid;
else l = mid+1;
}
//if((from^(1<<add)) == (1<<5)-1)cout<<add<<":"<<l<<' '<<r<<endl;
if(l)dp[to] = min(dp[to],dp[from]+f(from,pos[add][l-1],add));
else dp[to] = min(dp[to],dp[from]+f(from,0,add));
if(r)dp[to] = min(dp[to],dp[from]+f(from,pos[add][r-1],add));
else dp[to] = min(dp[to],dp[from]+f(from,0,add));
return;
}
int main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>s;
N = s.size();
s = "#"+s;
for(int i = 1;i<=N;i++){
pos[s[i]-'A'].push_back(i);
G = max(G,int(s[i]-'A'+1));
}
for(int i = 0;i<G;i++){
for(int j = 0;j<G;j++){
getprec(i,j);
}
}
cerr<<"PREC"<<endl;
fill(dp,dp+(1<<mxg),inf);
dp[0] = 0;
for(int i = 0;i<(1<<G);i++){
for(int j = 0;j<G;j++){
if(!(i&(1<<j)))trans(i,i^(1<<j),j);
}
}
cerr<<dp[(1<<G)-1]<<'\n';
cout<<fixed<<setprecision(20)<<double(dp[(1<<G)-1])/4.0<<'\n';
return 0;
}
