#include <bits/stdc++.h>
#define fr(i, a, b) for (int i = (a); i <= (b); ++i)
#define rf(i, a, b) for (int i = (a); i >= (b); --i)
#define fe(x, y) for (auto& x : y)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(), (x).end()
#define pw(x) (1LL << (x))
#define sz(x) (int)(x).size()
using namespace std;
mt19937_64 rng(228);
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
template <typename T>
using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define fbo find_by_order
#define ook order_of_key
template <typename T>
bool umn(T& a, T b) { return a > b ? a = b, 1 : 0; }
template <typename T>
bool umx(T& a, T b) { return a < b ? a = b, 1 : 0; }
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template <typename T>
using ve = vector<T>;
string s;
ve<int> v[26];
int main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#else
ios::sync_with_stdio(0);
cin.tie(0);
#endif
cin >> s;
// fr (i, 1, 899) s.pb('A');
fr (i, 0, sz(s) - 1) {
v[s[i] - 'A'].pb(i);
}
ve<int> p;
fr (i, 0, 25) {
if (sz(v[i])) {
p.pb(i);
}
}
ld res = 1e18;
ve<bool> act(sz(s));
ve<int> P(sz(s));
ve<int> S(sz(s));
ve<int> SS(sz(s));
ve<int> PP(sz(s));
do {
fill(all(act), 0);
ld ans = 0;
fe (x, p) {
fr (i, 0, sz(v[x]) - 1) {
PP[i] = P[v[x][i]];
if (i > 0) PP[i] += PP[i - 1];
}
rf (i, sz(v[x]) - 1, 0) {
SS[i] = S[v[x][i]];
if (i + 1 < sz(v[x])) SS[i] += SS[i + 1];
}
ld best = 1e18;
fr (pref, 0, sz(v[x])) {
ld now = 0;
if (pref - 1 >= 0) now += PP[pref - 1];
if (pref < sz(v[x])) now += SS[pref];
// fr (i, 0, pref - 1) {
// now += P[v[x][i]];
// }
// fr (i, pref, sz(v[x]) - 1) {
// now += S[v[x][i]];
// }
now += ld(0.5) * pref * (pref - 1) / 2;
int suff = sz(v[x]) - pref;
now += ld(0.5) * suff * (suff - 1) / 2;
// if (abs(now - 2) <= 1e-7) {
// cout << pref << " " << suff << "\n";
// }
umn(best, now);
}
fe (cur, v[x]) act[cur] = 1;
fr (i, 0, sz(s) - 1) {
P[i] = act[i];
if (i > 0) P[i] += P[i - 1];
}
rf (i, sz(s) - 1, 0) {
S[i] = act[i];
if (i + 1 < sz(s)) {
S[i] += S[i + 1];
}
}
// cout << "Add " << best << " " << char(x + 'A') << "\n";
ans += best;
}
// cout << "\n";
umn(res, ans);
} while (next_permutation(all(p)));
cout << fixed << setprecision(10) << res << "\n";
return 0;
}
