#include <bits/stdc++.h>
using namespace std;
const int maxn = 100005, maxg = 20;
int n, g;
string s;
double prosli[maxn][maxg];
int red[maxg];
double ukp[maxg], lijevo[maxn], desno[maxn], dodaj[maxn];
vector <int> mjesta[maxg];
double ans = 1e18;
int main (void){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cin >> s;
n = s.size();
memset(prosli, 0, sizeof prosli);
for (int i = 0; i < n; i++){
if (i != 0){
for (int j = 0; j < 15; j++) prosli[i][j] = prosli[i - 1][j];
}
int j = s[i] - 'A';
if (prosli[i][j] == 0) red[g] = j, g++;
prosli[i][j]++;
ukp[j]++;
mjesta[j].push_back(i);
}
sort(red, red + g);
int brojac = 0;
do{
brojac++;
double tr = 0;
for (int i = 0; i < n; i++) lijevo[i] = 0, desno[i] = 0, dodaj[i] = 0;
for (int i = 0; i < g; i++){
int x = red[i];
for (int j = 0; j < mjesta[x].size(); j++){
int y = mjesta[x][j];
tr += min(lijevo[y] + (prosli[y][x] - 1) / 2, desno[y] + (ukp[x] - prosli[y][x]) / 2);
}
for (int j = 0; j < mjesta[x].size(); j++) dodaj[mjesta[x][j]] = 1;
for (int j = 0; j < n; j++){
if (j == 0) lijevo[j] = dodaj[j];
else lijevo[j] = lijevo[j - 1] + dodaj[j];
}
for (int j = n - 1; j >= 0; j--){
if (j == n - 1) desno[j] = dodaj[j];
else desno[j] = desno[j + 1] + dodaj[j];
}
}
//cout << endl << tr << endl;
ans = min(ans, tr);
//if (tr == 10.5) cout << red[0] << red[1] << red[2] << red[3] << red[4] << endl;
}while (next_permutation(red, red + g));
cout << fixed << setprecision(10);
cout << ans << "\n";
return 0;
}
