/*
* File created on 07/19/2022 at 18:21:46.
* Link to problem:
* Description:
* Time complexity: O()
* Space complexity: O()
* Status: ---
* Copyright: Ⓒ 2022 Francois Vogel
*/
#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;
#define pii pair<int, int>
#define f first
#define s second
#define vi vector<int>
#define all(x) x.begin(), x.end()
#define size(x) (int)((x).size())
#define pb push_back
#define ins insert
#define cls clear
#define int ll
#define ll long long
#define ld long double
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
const int inf = 1e18;
signed main() {
cin.tie(0);
ios_base::sync_with_stdio(0);
cout.precision(20);
string b;
cin >> b;
const int n = size(b);
int gK = 0;
for (char i : b) if (i-'A'+1 > gK) gK = i-'A'+1;
vi per [gK];
for (int i = 0; i < n; i++) {
per[b[i]-'A'].pb(i);
}
ld cost [gK][1<<gK];
for (int i = 0; i < gK; i++) for (int j = 0; j < (1<<gK); j++) if (!((j>>i)&1)) {
int pref [n];
for (int k = 0; k < n; k++) pref[k] = (j>>(b[k]-'A'))&1;
for (int k = 1; k < n; k++) pref[k] += pref[k-1];
cost[i][j] = 0;
for (int k = 0; k < size(per[i]); k++) {
ld dl = k;
ld dr = size(per[i])-k-1;
ld cl = 0;
if (per[i][k]) cl = pref[per[i][k]-1];
ld cr = pref[n-1]-pref[per[i][k]];
cost[i][j] += min(cl+dl/(ld)(2), cr+dr/(ld)(2));
}
}
ld dp [1<<gK];
dp[(1<<gK)-1] = 0;
for (int i = (1<<gK)-2; i >= 0; i--) {
dp[i] = inf;
for (int j = 0; j < gK; j++) if (!((i>>j)&1)) {
dp[i] = min(dp[i], dp[i|(1<<j)]+cost[j][i]);
}
}
cout << dp[0];
cout.flush();
int d = 0;
d++;
}
