#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::steady_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
string s;
cin >> s;
int n = sz(s);
set<char> xd;
for(auto ele : s){
xd.insert(ele);
}
int g = sz(xd);
vector<char> vec;
for(auto ele : xd){
vec.pb(ele);
}
if(g == 1){
ld ans = (ld)(n / 2) * (n / 2 - 1) / 4 + (ld)(n - n / 2) * (n - n / 2 - 1) / 4;
cout << fixed << setprecision(5) << ans << '\n';
return 0;
}
vi p;
for(int i = 0; i < g; i++){
p.pb(i);
}
ld ans = 1e18;
do{
//cout << "----\n";
ld akt = 0;
vi ok(n, 0);
for(int i = 0; i < g; i++){
vll toLeft;
int now = 0;
for(int j = 0; j < n; j++){
if(s[j] == vec[p[i]]){
toLeft.pb((ll)now + (sz(toLeft) > 0 ? toLeft.back() : 0LL));
}else if(ok[j]){
now++;
}
}
vll toRight(sz(toLeft), 0LL);
int wsk = sz(toLeft) - 1;
now = 0;
for(int j = n - 1; j >= 0; j--){
if(s[j] == vec[p[i]]){
toRight[wsk] = (ll)now + (wsk < sz(toLeft) - 1 ? toRight[wsk + 1] : 0LL);
wsk--;
ok[j] = 1;
}else if(ok[j]){
now++;
}
}
int m = sz(toLeft);
ld add = (ld)m * (m - 1) / 4 + toRight[0];
for(int j = 0; j < m; j++){
ld no = (ld)j * (j + 1) / 4 + (ld)(m - j - 1) * (m - j - 2) / 4;
no += toLeft[j];
no += ((j < m - 1 ? toRight[j + 1] : 0LL));
add = min(add, no);
}
akt += add;
}
ans = min(ans, akt);
}while(next_permutation(all(p)));
cout << fixed << setprecision(8) << ans << '\n';
return 0;
}
