#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int nx=1e5+5, kx=15;
ll n, p[kx][kx][nx], dp[(1<<kx)+5];
string s;
vector<ll> d[kx];
int main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>s;
n=s.size();
s=' '+s;
for (int i=0; i<kx; i++) d[i].push_back(0);
for (int i=1; i<=n; i++) d[s[i]-'A'].push_back(i);
for (int i=0; i<kx; i++)
{
for (int j=0; j<kx; j++)
{
ll v=(i==j)?1:2, tmp=0, cnt=0;
vector<ll> pref(n+2), suf(n+2);
for (int k=1; k<=n; k++)
{
if (s[k]-'A'==i) cnt+=tmp;
if (s[k]-'A'==j) tmp+=v;
pref[k]=cnt;
}
tmp=cnt=0;
for (int k=n; k>=1; k--)
{
if (s[k]-'A'==i) cnt+=tmp;
if (s[k]-'A'==j) tmp+=v;
suf[k]=cnt;
}
for (int k=0; k<=n; k++) p[i][j][k]=pref[k]+suf[k+1];
}
}
for (int i=1; i<(1<<kx); i++)
{
dp[i]=LLONG_MAX;
for (int j=0; j<kx; j++)
{
if (i&(1<<j))
{
ll l=0, r=d[j].size()-1;
while (l<r)
{
ll md=(l+r)/2, df=0;
for (int k=0; k<kx; k++) if (i&(1<<k)) df+=p[j][k][d[j][md+1]]-p[j][k][d[j][md]];
if (df>=0) r=md;
else l=md+1;
}
//cout<<"here "<<d[j][l]<<'\n';
ll vl=0;
for (int k=0; k<kx; k++) if (i&(1<<k)) vl+=p[j][k][d[j][l]];
dp[i]=min(dp[i], dp[i^(1<<j)]+vl);
}
}
//cout<<"dp "<<i<<' '<<dp[i]<<'\n';
}
printf("%.4f\n", dp[((1<<kx)-1)]/2.0);
}
