#include<bits/stdc++.h>
#define pb push_back
#define all(v) v.begin(),v.end()
#define forf(i,s,e) for(int i = s; i<=e; i++)
#define forb(i,s,e) for(int i = s; i>=e; i--)
#define idx(i,v) lower_bound(all(v),i)-v.begin()
#define comp(v) v.erase(unique(all(v)),v.end())
#define sz(v) (int)v.size()
#define fs first
#define se second
#define SP << " " <<
#define LN << "\n"
#define IO cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false);
using namespace std;
typedef long long ll;
ll inf = 1e18;
int N,M; string S;
vector<char> chars;
vector<int> pos[16];
int G[100001];
vector<double> f[16][16];
double dp[1<<15];
double eval(int now, int bit, int idx){
double ret = 0;
forf(i,0,M-1){
if(!(bit & ( 1<<i))) continue;
if(i==now) ret += f[now][i][idx]/2;
else ret += f[now][i][idx];
}
return ret;
}
double calc(int now, int bit){
int l = -1, r = sz(f[now][now])-1;
while(l+1<r){
int m = l+r>>1;
if(eval(now,bit,m) < eval(now,bit,m+1)) r = m;
else l = m;
}
return eval(now,bit,r);
}
int main(){
cin>>S; N = sz(S);
forf(i,0,N-1) chars.pb(S[i]);
sort(all(chars)), comp(chars);
forf(i,0,N-1) G[i] = idx(S[i], chars), pos[G[i]].pb(i);
M = sz(chars);
forf(i,0,M-1){
forf(j,0,M-1){
f[i][j].resize(sz(pos[i])+1,0);
for(auto u : pos[i]){
f[i][j][0] += pos[j].end() - upper_bound(all(pos[j]), u);
}
int idx = 1;
for(auto u : pos[i]){
f[i][j][idx] = f[i][j][idx-1];
f[i][j][idx] -= pos[j].end() - upper_bound(all(pos[j]),u);
f[i][j][idx] += lower_bound(all(pos[j]), u) - pos[j].begin();
idx++;
}
}
}
forf(i,1,(1<<M)-1) dp[i] = inf;
forf(now,1,(1<<M)-1){
forf(b,0,M-1){
if(!(now&(1<<b))) continue;
int prv = now^(1<<b);
dp[now] = min(dp[now], dp[prv] + calc(b,now));
}
}
cout.precision(100);
cout<< dp[(1<<M)-1];
}
