#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#define FAST_IO ios::sync_with_stdio(false);cin.tie(0);
#define pb push_back
#define all(x) begin(x), end(x)
#define space " "
#define TEST_CASES int a; cin >> a; for (int i = 0; i < a; i++) {solve(); cout << endl;}
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
void solve() {
string s; cin >> s; int n = s.size();
vector<int> vec(n);
vector<vector<int>> alph(15);
for (int i = 0; i < n; i++) {
vec[i] = s[i] - 'A';
alph[vec[i]].pb(i);
}
vector<vector<vector<ll>>> lefts(15, vector<vector<ll>>(15));
vector<vector<vector<ll>>> rights(15, vector<vector<ll>>(15));
for (int i = 0; i < 15; i++) {
ll curr = 0; ll curr2 = 0;
for (int j = 0; j < n; j++) {
if (vec[j] == i) {
curr++;
}
lefts[vec[j]][i].pb(curr + (lefts[vec[j]][i].empty() ? 0 : lefts[vec[j]][i].back()));
}
for (int j = n - 1; j >= 0; j--) {
if (vec[j] == i) {
curr2++;
}
rights[vec[j]][i].pb(curr2 + (rights[vec[j]][i].empty() ? 0 : rights[vec[j]][i].back()));
}
}
vector<ld> dp(1 << 15, (ll)n * (n - 1) / 2);
auto check = [&] (int subset, int letter, int split) -> ld {
ll num = alph[letter].size();
ld res = 0;
for (int i = 0; i < 15; i++) {
if (subset & 1 << i) {
res += (split == -1 ? 0 : lefts[letter][i][split]) +
(split != num - 1 ? rights[letter][i][num - split - 2] : 0);
}
}
res += (ld)split * (split + 1) / 4 + (ld)(num - split - 1) * (num - split - 2) / 4;
return res;
};
dp[0] = 0;
for (int i = 1; i < 1 << 15; i++) {
for (int j = 0; j < 15; j++) {
if (i & 1 << j) {
if (!alph[j].empty()) {
int lo = -1; int hi = alph[j].size() - 1;
while (lo < hi) {
int mid = (lo + hi) / 2; int next = mid + 1;
if (lo == -1 && hi == 0) {
mid = -1; next = 0;
}
ld r1 = check(i ^ 1 << j, j, mid); ld r2 = check(i ^ 1 << j, j, next);
if (r2 <= r1) {
lo = next;
}
else {
hi = mid;
}
}
dp[i] = min(dp[i], dp[i ^ 1 << j] + check(i ^ 1 << j, j , lo));
}
else {
dp[i] = min(dp[i], dp[i ^ 1 << j]);
}
}
}
}
cout << fixed << setprecision(10);
cout << dp.back();
}
int main() {
FAST_IO;
//freopen("lightsout.in", "r", stdin);
//freopen("lightsout.out", "w", stdout);
//TEST_CASES;
solve(); cout << endl;
/*int a; cin >> a;
for (int i = 1; i <= a; i++){
cout << "Case #" << i << ": ";
solve();
cout << endl;
}*/
}
