#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
void solve(int test_case)
{
string s; cin >> s;
ll n = sz(s);
s = "$" + s;
ll siz = 0;
rep1(i,n){
amax(siz,(ll)s[i]-'A'+1);
}
vector<ll> pos[siz];
rep1(i,n) pos[s[i]-'A'].pb(i);
vector<ll> add_pref[siz][siz], add_suff[siz][siz];
vector<ll> pref(n+5);
rep(x,siz){
fill(all(pref),0);
trav(i,pos[x]){
pref[i]++;
}
rep1(i,n) pref[i] += pref[i-1];
rep(y,siz){
if(x == y) conts;
trav(i,pos[y]){
add_pref[x][y].pb(pref[i]);
add_suff[x][y].pb(pref[n]-pref[i]);
}
}
}
vector<ll> dp(1<<siz,inf2);
dp[0] = 0;
rep(mask,1<<siz){
vector<ll> seated;
rep(c,siz){
if(mask&(1<<c)){
seated.pb(c);
}
}
rep(c,siz){
if(mask&(1<<c)) conts;
ll sizp = sz(pos[c]);
ll s1 = 0, s2 = sizp;
ll cost1 = 0, cost2 = 0;
rep(i,sizp){
trav(d,seated){
cost2 += add_suff[d][c][i];
}
}
ll mn_cost = inf2;
amin(mn_cost,s2*(s2-1)+cost2*4);
rep(i,sizp){
s1++, s2--;
trav(d,seated){
cost1 += add_pref[d][c][i];
cost2 -= add_suff[d][c][i];
}
amin(mn_cost,s1*(s1-1)+s2*(s2-1)+cost1*4+cost2*4);
}
amin(dp[mask|(1<<c)],dp[mask]+mn_cost);
}
}
ld ans = (ld)dp[(1<<siz)-1]/4;
cout << fixed << setprecision(11);
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
