#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define all(x) (x).begin(), (x).end()
#define MP make_pair
const int N = 100500;
long long exp_inv(ll n){
return (long long) n * (n - 1); // should be divided by 4
}
ll dp[1 << 15];
void solve(){
string s;
cin >> s;
int n = (int)s.size();
vector<vector<int>> pos;
map<char, int> id;
for (int i = 0; i < n; i++){
if (id.find(s[i]) == id.end()){
id[s[i]] = (int) id.size();
pos.emplace_back();
}
pos[id[s[i]]].push_back(i);
}
int G = (int) pos.size();
fill(dp, dp + (1 << G), 5e18);
dp[0] = 0;
for (int mask = 0; mask < (1 << G); mask++){
if (dp[mask] >= 1e18) continue;
vector<int> cnt(n, 0);
for (int c = 0; c < G; c++){
if (mask & (1 << c)){
for (int i : pos[c]) cnt[i] = 1;
}
}
for (int i = 1; i < n; i++) cnt[i] += cnt[i - 1];
for (int c = 0; c < G; c++){
if (mask & (1 << c)) continue;
int sz = (int) pos[c].size();
long long mn = 5e18;
for (int half = 0; half <= sz; half++){
ll cur = 0;
for (int i = 0; i < sz; i++){
int j = pos[c][i];
if (i < half){
cur += cnt[j];
} else {
cur += cnt.back() - cnt[j];
}
}
cur *= 4;
cur += exp_inv(half) + exp_inv(sz - half);
mn = min(mn, cur);
}
int new_mask = mask | (1 << c);
dp[new_mask] = min(dp[new_mask], dp[mask] + mn);
}
}
cout << fixed << setprecision(5);
cout << (long double) dp[(1 << G) - 1] / 4 << endl;
}
int main() {
ios_base::sync_with_stdio(false);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
solve();
return 0;
}
