#include<bits/stdc++.h>
using namespace std;
#define int long long
const int inf=1e18;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
string s;
cin >> s;
int n=s.size();
vector<int> a(n);
map<int, int> num; int ind=1;
vector<vector<int> > group(15, vector<int> (1, 0));
for(int i=0; i<n; i++){
if(num[s[i]]==0){
num[s[i]]=ind;
ind++;
}
a[i]=num[s[i]]-1;
group[a[i]].push_back(i);
}
int g=ind-1;
for(int i=0; i<15; i++){
group[i].push_back(n-1);
}
vector<vector<int> > prefix(n+1, vector<int> (g, 0));
vector<vector<int> > suffix(n+1, vector<int> (g, 0)); //exklusiv
for(int i=0; i<n; i++){
prefix[i+1]=prefix[i];
prefix[i+1][a[i]]++;
}
for(int i=n-1; i>0; i--){
suffix[i-1]=suffix[i];
suffix[i-1][a[i]]++;
}
vector<vector<vector<int> > > prefixsum(n+1, vector<vector<int> > (g, vector<int> (g, 0)));
vector<vector<vector<int> > > suffixsum(n+1, vector<vector<int> > (g, vector<int> (g, 0)));
for(int i=1; i<n; i++){
prefixsum[i]=prefixsum[i-1];
for(int j=0; j<g; j++){
prefixsum[i][a[i]][j]+=prefix[i][j];
}
}
for(int i=n-2; i>=0; i--){
suffixsum[i]=suffixsum[i+1];
for(int j=0; j<g; j++){
suffixsum[i][a[i]][j]+=suffix[i][j];
}
}
auto cost=[&](int mask, int lastgroup, int lastleft){
if(lastleft+1==(int)group[lastgroup].size()){
return inf;
}
int indleft=group[lastgroup][lastleft];
int indright=group[lastgroup][lastleft+1];
//cout << "left: " << indleft << " right: " << indright << "\n" << flush;
int ans=0;
for(int i=0; i<g; i++){
if((mask>>i)%2==0 || i==lastgroup) continue;
ans+=prefixsum[indleft][lastgroup][i]*2;
ans+=suffixsum[indright][lastgroup][i]*2;
}
ans+=prefixsum[indleft][lastgroup][lastgroup];
ans+=suffixsum[indright][lastgroup][lastgroup];
return ans;
};
auto mincost=[&](int mask, int lastgroup){
//cout << "mincost:\n";
//cout << "mask: " << mask << " last group: " << lastgroup << "\n";
int l=0; int r=group[lastgroup].size()-2;
int ans=r;
while(l<=r){
//cout << "bs " << l << " " << r << "\n" << flush;
int m=l+(r-l)/2;
if(cost(mask, lastgroup, m)<=cost(mask, lastgroup, m+1)){
ans=m;
r=m-1;
}
else{
l=m+1;
}
}
//cout << "mincost " << mask << " " << lastgroup << " " << ans << " " << cost(mask, lastgroup, ans) << "\n" << flush;
return cost(mask, lastgroup, ans);
};
vector<int> dp((1<<g), inf);
dp[0]=0;
for(int i=1; i<(1<<g); i++){
for(int last=0; last<g; last++){
if((i>>last)%2==0) continue;
dp[i]=min(dp[i], dp[i-(1<<last)]+mincost(i, last));
}
//cout << i << " " << dp[i] << "\n" << flush;
}
double ans=(double)dp[(1<<g)-1]/(double)2;
cout.precision(100);
cout << ans << "\n";
}
