#include <bits/stdc++.h>
using namespace std;
// ordered set whith s.order_of_key(x) method, which returns rank of element x in set s
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
*/
// pair printing
template <class T, class U>
ostream& operator<<(ostream& out, const pair<T, U> &par) {out << "(" << par.first << "; " << par.second << ")"; return out;}
// set printing
template <class T>
ostream& operator<<(ostream& out, const set<T> &cont) { out << "{"; for(const auto &x:cont) out << x << ", "; out << "}"; return out; }
// map printing
template <class T, class U>
ostream& operator<<(ostream& out, const map<T, U> &cont) {out << "{"; for(const auto &x:cont) out << x << ", "; out << "}"; return out; }
// unordered_set printing
template <class T>
ostream& operator<<(ostream& out, const unordered_set<T> &cont) {out << "{";for(const auto &x:cont) out << x << ", ";out << "}";return out;}
// unordered_map printing
template <class T, class U>
ostream& operator<<(ostream& out, const unordered_map<T, U> &cont) {out << "{";for(const auto &x:cont) out << x << ", ";out << "}";return out;}
// vector printing
template<class T>
ostream& operator<<(ostream& out, const vector<T> &cont){ out << "["; for (const auto &x:cont) out << x << ", "; out << "]"; return out;}
#define print(x) cout << (x) << endl;
#define dmp(x) cerr << #x << " = " << x << endl
#define dmpn(x) cerr << #x << " = " << x << "; "
#define dmpl(x) cerr << "Line " << __LINE__ << ": " << #x << " = " << x << endl
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define pb push_back
#define ff first
#define ss second
#define all(x) begin(x), end(x)
#define sz(x) (int)x.size()
#define contains(s,x) ((s).find(x) != (s).end())
const int MOD = 998244353;
bool ith_bit(int x, int i) {
int y = (1 << i);
return (x ^ y) < x;
}
void print_bits(int x) {
bitset<8> bx = x;
cout << bx << endl;
}
void solve() {
string s;
cin >> s;
int N = sz(s);
vector<int> mapping(26, -1);
int M = 0;
for (int i = 0; i < N; i++) {
if (mapping[s[i] - 'A'] == -1) {
mapping[s[i] - 'A'] = M;
M++;
}
}
int M2 = (1 << M);
vector<ld> dp(M2, N * N);
dp[0] = 0;
for (int mask = 1; mask < M2; mask++) {
// print_bits(mask);
for (int i = 0; i < M; i++) if (ith_bit(mask, i) == 1) {
// dmp(i);
int i2 = 1 << i;
vector<int> a(N, 0);
int suff_sum = 0;
for (int j = 0; j < N; j++) {
if (ith_bit(mask, mapping[s[j] - 'A'])) {
if (mapping[s[j] - 'A'] == i) a[j] = 1;
else a[j] = 2;
}
suff_sum += a[j];
}
// dmp(a);
ld prev = dp[mask ^ i2], curr = 0;
int pref_sum = 0;
for (int j = 0; j < N; j++) {
suff_sum -= a[j];
if (mapping[s[j] - 'A'] == i) {
ld val = (ld)min(pref_sum, suff_sum) / (ld)2;
curr += val;
}
pref_sum += a[j];
}
dp[mask] = min(dp[mask], prev + curr);
}
}
ld ans = dp[M2 - 1];
cout << ans << endl;
}
int32_t main() {
ios::sync_with_stdio(false);
cout << setprecision(12);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
