#include <bits/stdc++.h>
using namespace std;
using ll = int;
using vll = vector<ll>;
using vvl = vector<vll>;
using pll = pair<ll,ll>;
using vpl = vector<pll>;
using vvp = vector<vpl>;
using vd = vector<vector<pll>>;
#define f first
#define s second
#define pb push_back
#define all(v) v.begin(),v.end()
struct seg{
ll n;
vll bl;
seg(ll n):n(n){
bl = vll(n*2);
}
void upd(ll i, ll x){
i+=n;
bl[i]+=x;
for(i/=2;i>0;i/=2){
bl[i] = bl[i*2]+bl[i*2+1];
}
}
ll que(ll a, ll b){
ll ans = 0;
for(a+=n,b+=n;a<=b;a/=2, b/=2){
if(a&1)ans += bl[a++];
if(!(b&1))ans += bl[b--];
}
return ans;
}
};
ll m=0;
int main(){
ios_base::sync_with_stdio(0);cin.tie(NULL);
string s;
cin >> s;
ll n = s.size();
vll ch(26,-1);
for(char i:s){
if(ch[i-'A']==-1){
ch[i-'A']=m++;
}
}
vvl g(m);
for(ll i = 0; i < n; ++i){
g[ch[s[i]-'A']].pb(i);
}
ll N = 1 << (32-__builtin_clz(n-1));
seg *S = new seg(N);
vd tb(m, vector<pll>(n));
for(ll i = 0; i < m; ++i){
for(ll h: g[i])S->upd(h, 1);
for(ll j = 0; j < m; ++j){
if(i!=j){
for(ll h:g[j]){
tb[i][h].f += 2*S->que(0, h-1);
tb[i][h].s += 2*S->que(h+1, n-1);
}
}
else{
for(ll h:g[j]){
tb[i][h].f += S->que(0, h-1);
tb[i][h].s += S->que(h+1, n-1);
}
}
}
for(ll h: g[i])S->upd(h, -1);
}
vector<vector<double>> gtg(1<<m, vector<double>(m));
for(ll i = 0; i < (1<<m); ++i){
for(ll j = 0; j < m; ++j){
if(!(i & (1<<j)))continue;
for(ll k:g[j]){
pll tr = {0,0};
for(ll h = 0; h < m; ++h){
if(!(i & (1<<h)))continue;
tr.f += tb[h][k].f;
tr.s += tb[h][k].s;
}
gtg[i][j] += min(tr.f, tr.s);
}
}
}
vector<double> dp(1<<m, 1e11);
dp[0]=0;
for(ll i = 1; i < (1<<m); ++i){
for(ll j = 0; j < m; ++j){
if(i & (1<<j)){
dp[i] = min(dp[i], dp[i ^ (1<<j)] + gtg[i][j]);
}
}
}
cout << fixed << setprecision(6) << (double)dp[(1<<m)-1]/2;
}
