#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main(){
// random_device rd;
// mt19937 rng(rd());
ios::sync_with_stdio(false);
cin.tie(nullptr);
string s;
cin >> s;
int n = s.size();
vector<vector<int>> points(15);
vector<int> pool;
for (int i = 0; i < n; ++i) {
int j = s[i] - 'A';
pool.push_back(j);
}
sort(begin(pool), end(pool));
pool.erase(unique(begin(pool), end(pool)), end(pool));
map<char, int> mp;
for (int i = 0; i < pool.size(); ++i) {
mp[(pool[i] + 'A')] = i;
}
vector<vector<int>> cnt(15, vector<int>(n + 1));
for (int i = 0; i < n; ++i) {
points[mp[s[i]]].push_back(i);
for (int j = 0; j < 15; ++j) {
cnt[j][i + 1] = cnt[j][i] + (j == mp[s[i]]);
}
}
// for (int j = 0; j < 2; ++j) {
// for (int i = 0; i < n; ++i) {
// cout << cnt[j][i] << " ";
// }
// cout << endl;
// }
int k = pool.size();
vector<vector<double>> nxt((1 << k), vector<double>(k));
// cerr << "BEGIN:\n";
for (int i = 0; i < k; ++i) {
// cerr << "A\n";
auto v = points[i];
vector<vector<ll>> L(k, vector<ll>(v.size())), R(k, vector<ll>(v.size()));
for (int j = 0; j < k; ++j) {
for (int l = 0; l < v.size(); ++l) {
L[j][l] = cnt[j][v[l]];
if (l > 0) L[j][l] += L[j][l - 1];
}
for (int l = v.size() - 1; l >= 0; --l) {
R[j][l] = cnt[j][n] - cnt[j][v[l] + 1];
if (l + 1 < v.size()) R[j][l] += R[j][l + 1];
}
}
// cerr << "B\n";
for (int j = 0; j < (1 << k); ++j) {
if (j >> i & 1) continue;
auto calc = [&](ll l) -> double {
double res = 0;
for (int x = 0; x < k; ++x) {
if (j >> x & 1) {
if (l > 0) res += L[x][l - 1];
if (l < v.size()) res += R[x][l];
}
}
res += 1.0 * l * (l - 1) / 4.0;
ll r = v.size() - l;
res += 1.0 * r * (r - 1) / 4.0;
return res;
};
int l = 0, r = v.size();
while (l < r) {
int mid = (l + r) / 2;
if (calc(mid) > calc(mid + 1)) {
l = mid + 1;
} else {
r = mid;
}
}
nxt[j][i] = calc(l);
}
// cerr << "C\n";
}
// cerr << "END\n";
vector<double> dp((1 << k), 1e15);
dp[0] = 0;
for (int mask = 0; mask < (1 << k); ++mask) {
if (dp[mask] == 1e15) continue;
for (int j = 0; j < k; ++j) {
if (mask >> j & 1) continue;
// cout << "NOW = " << char(j + 'A') << "\n";
double ndp = dp[mask] + nxt[mask][j];
dp[mask | (1 << j)] = min(dp[mask | (1 << j)], ndp);
}
}
cout << fixed << setprecision(10) << dp[(1 << k) - 1] << endl;
}
