#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
int pre[100010][20],pr[100010][20][20],su[100010][20][20];
ld cost[100010];
ld dp[100010];
vector<int> place[20];
ld getcost(int pos,int num,int k){
//cerr<<pos<<' '<<num<<' '<<k<<"\n";
int n=place[k].size()-1;
ld ret=cost[pos+1]+cost[n-pos];
for (int i=0;i<15;i++){
if ((num&(1<<i))==0) continue;
if (pos<n) ret+=su[place[k][pos+1]][k][i];
if (pos>-1) ret+=pr[place[k][pos]][k][i];
}
return ret;
}
ld cacu(int num,int k){
int l=-1,r=place[k].size()-1;
//cerr<<l<<' '<<r<<"\n";
while (l+5<r){
int ml=l+(r-l)/3,mr=l+(r-l)/3*2;
//cerr<<l<<' '<<r<<' '<<ml<<' '<<mr<<"\n";
if (getcost(ml,num,k)<=getcost(mr,num,k)) r=mr;
else l=ml;
}
ld ret=1e18;
for (int i=l;i<=r;i++) ret=min(getcost(i,num,k),ret);
return ret;
}
signed main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
string s;cin>>s;s=' '+s;
int n=s.size()-1;
for (int i=1;i<=n;i++){
for (int j=0;j<15;j++) pre[i][j]=pre[i-1][j];
pre[i][s[i]-'A']++;
place[s[i]-'A'].push_back(i);
}
for (int i=2;i<=n;i++){
cost[i]=(cost[i-1]+(ld)(i-1)/2);
}
for (int i=1;i<=n;i++){
for (int j=0;j<15;j++){
for (int k=0;k<15;k++){
pr[i][j][k]=pr[i-1][j][k];
}
}
for (int k=0;k<15;k++) pr[i][s[i]-'A'][k]+=pre[i][k];
}
for (int i=n;i>0;i--){
for (int j=0;j<15;j++){
for (int k=0;k<15;k++){
su[i][j][k]=su[i-1][j][k];
}
}
for (int k=0;k<15;k++) su[i][s[i]-'A'][k]+=pre[n][k]-pre[i-1][k];
}
dp[0]=0;
for (int i=1;i<(1<<15);i++) dp[i]=1e18;
for (int i=1;i<(1<<15);i++){
for (int j=0;j<15;j++){
if ((i&(1<<j))==0) continue;
//cerr<<i<<' '<<j<<"\n";
dp[i]=min(dp[i^(1<<j)]+cacu(i^(1<<j),j),dp[i]);
}
//cout<<dp[i]<<"\n";
}
printf("%.6Lf\n",dp[(1<<15)-1]);
}
