#include <bits/stdc++.h>
using namespace std;
using ll = long long;
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);
vector<vvl> rs(m, vvl(m,{0}));
vector<vvl> sf(m, vvl(m,{0}));
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]){
rs[i][j].pb(2*S->que(0, h-1)+rs[i][j].back());
}
for(ll o = g[j].size()-1; o >= 0; --o){
ll h = g[j][o];
sf[i][j].pb(2*S->que(h+1, n-1)+sf[i][j].back());
}
}
else{
for(ll h:g[j]){
rs[i][j].pb(rs[i][j].back()+S->que(0, h-1));
}
for(ll o = g[j].size()-1; o >= 0; --o){
ll h = g[j][o];
sf[i][j].pb(sf[i][j].back()+S->que(h+1, n-1));
}
}
reverse(all(sf[i][j]));
}
for(ll h: g[i])S->upd(h, -1);
}
vvl gtg(1<<m, vll(m));
for(ll i = 0; i < (1<<m); ++i){
for(ll j = 0; j < m; ++j){
if(!(i & (1<<j)))continue;
ll s=0, e=g[j].size();
while(s<e){
ll m1 = (2*s+e)/3;
ll m2 = (s+e*2+1)/3;
ll c1=0,c2=0;
for(ll h = 0; h < m; ++h){
if(i&(1<<h)){
c1 += rs[h][j][m1]+sf[h][j][m1];
c2 += rs[h][j][m2]+sf[h][j][m2];
}
}
if(c1>c2)s=m1+1;
else e=m2-1;
gtg[i][j]=min(c1,c2);
}
}
}
vll 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;
}
