#include <bits/stdc++.h>
#define int long long
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
using namespace std;
unordered_map<char,int> um;
vector<vector<vector<int>>> cnt;
vector<vector<int>> val;
vector<int> dp;
vector<vector<int>> grp;
int n,g;
int calc(int l, int _g, int mask){
int lft=((l+1)*l)/2;
int r=(sz(grp[_g])-l-1);
int rgt=((r-1)*r)/2;
if(l>=0){
for (int i = 0; i < g; i++)
{
if(mask&(1<<i)) lft+=cnt[grp[_g][l]][i][0]*2;
}
}
if(l+1<sz(grp[_g])){
for (int i = 0; i < g; i++)
{
if(mask&(1<<i)) rgt+=cnt[grp[_g][l+1]][i][1]*2;
}
}
return lft+rgt;
}
int dfs(int mask){
if(dp[mask]!=-1) return dp[mask];
dp[mask]=1e18;
int mnI=0;
for (int i = 0; i < g; i++)
{
if(mask&(1<<i)) {
int r=dfs(mask-(1<<i))+val[i][mask-(1<<i)];
if(r<dp[mask]) mnI=i;
dp[mask]=min(dp[mask],r);
}
}
//cerr << mask << "-> " << mnI << " = " << dp[mask] << "\n";
return dp[mask];
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(nullptr);
string s; cin >> s;
n=sz(s);
vector<int> a(n);
for (int i = 0; i < n; i++)
{
if(um.find(s[i])==um.end()) um[s[i]]=sz(um);
a[i]=um[s[i]];
}
g=sz(um);
val.resize(g, vector<int>((1<<g),1e18));
dp.resize((1<<g),-1);
cnt.resize(n, vector<vector<int>>(g, vector<int>(2,0)));
grp.resize(g);
for (int i = 0; i < n; i++) grp[a[i]].push_back(i);
for (int i = 0; i < g; i++)
{
for (int j = 0; j < g; j++)
{
int sm=0;
int sm_cnt=0;
for (int k = 0; k < n; k++)
{
if(a[k]==i) cnt[k][j][0]=sm+sm_cnt, sm_cnt+=sm;
if(a[k]==j) sm++;
}
sm=0;
sm_cnt=0;
for (int k = n-1; k >= 0; k--)
{
if(a[k]==i) cnt[k][j][1]=sm+sm_cnt, sm_cnt+=sm;
if(a[k]==j) sm++;
}
}
}
for (int i = 0; i < g; i++)
{
for (int mask = 0; mask < (1<<g); mask++)
{
if(mask&(1<<i)) continue;
int l=-1, r=sz(grp[i])-1;
while(r-l>2){
int mid1=l+(r-l)/3;
int mid2=r-(r-l)/3;
if(calc(mid1, i, mask)<calc(mid2, i, mask)){
r=mid2;
}else{
l=mid1;
}
}
for (int j = l; j <= r; j++)
{
val[i][mask]=min(val[i][mask], calc(j, i, mask));
}
}
}
dp[0]=0;
long double ret=(long double)dfs((1<<g)-1)/(long double)2;
cout << fixed << setprecision(1) << (long double)ret << "\n";
return 0;
}
