#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 100100;
const int K = 15;
ll p[N][K];
ll q[N][K][K];
ll s[N][K][K];
ll dp[1 << K];
vector<int> pos[K];
void solve() {
string str;
cin >> str;
int n = str.size();
vector<int> v(n);
for (int i = 0; i < n; ++i) {
v[i] = str[i] - 'A';
pos[v[i]].push_back(i);
}
for (int k = 0; k < K; ++k) pos[k].push_back(n);
for (int i = 0; i < n; ++i) {
for (int k = 0; k < K; ++k) p[i+1][k] = p[i][k] + (v[i] == k);
for (int k = 0; k < K; ++k) {
for (int l = 0; l < K; ++l) q[i+1][k][l] = q[i][k][l] + (v[i] == k) * p[i+1][l];
}
}
for (int i = n-1; i >= 0; --i) {
for (int k = 0; k < K; ++k) {
for (int l = 0; l < K; ++l) s[i][k][l] = s[i+1][k][l] + (v[i] == k) * (p[n][l] - p[i][l]);
}
}
memset(dp, 0x3f, sizeof dp);
dp[0] = 0;
for (int j = 1; j < (1 << K); ++j) {
for (int i = 0; i < K; ++i) if (j >> i & 1) {
int a = -1, d = pos[i].size();
ll ans = 1e18;
while (d-a > 2) {
int b = a + (d-a)/3;
int c = a + 2*(d-a)/3;
int x = pos[i][b];
int y = pos[i][c];
ll ansb = p[x][i]*(p[x][i]-1)/2 + (p[n][i]-p[x][i])*(p[n][i]-p[x][i]-1)/2;
ll ansc = p[y][i]*(p[y][i]-1)/2 + (p[n][i]-p[y][i])*(p[n][i]-p[y][i]-1)/2;
for (int k = 0; k < K; ++k) if (i != k && (j >> k & 1)) {
ansb += 2*q[x][i][k] + 2*s[x][i][k];
ansc += 2*q[y][i][k] + 2*s[y][i][k];
}
if (ansb < ansc) {
ans = min(ans, ansb);
d = c;
} else {
ans = min(ans, ansc);
a = b;
}
}
dp[j] = min(dp[j], dp[j ^ (1 << i)] + (p[n][i] > 0) * ans);
}
}
cout << (long double) dp[(1 << K) - 1] / 2.0 << '\n';
}
int main() {
cin.tie(0) -> sync_with_stdio(0);
cout << fixed << setprecision(6);
solve();
}
