#include <bits/stdc++.h>
using namespace std;
const int maxn = 100005, maxg = 15;
int n, g;
string s;
double prosli[maxn][maxg], dp[1 << maxg];
int red[maxg], red2[maxg];
double ukp[maxg], calcb[maxg][maxg][maxn], calcf[maxg][maxg][maxn];
vector <int> mjesta[maxg];
double ans = 1e18;
int binary_search (int x, int mask){
int low = 0, high = ukp[red[x]], mid, mid2;
while (low < high){
//cout << low << " " << high << endl;
mid = (low + high) / 2;
mid2 = mid + 1;
double suma = 0, suma2 = 0;
double m = mid, m2 = mid2;
suma += m * (m - 1) / 2;
suma += (ukp[red[x]] - m) * (ukp[red[x]] - m - 1) / 2;
suma = suma / 2;
suma2 += mid2 * (m2 - 1) / 2;
suma2 += (ukp[red[x]] - m2) * (ukp[red[x]] - m2 - 1) / 2;
suma2 = suma2 / 2;
for (int j = 0; j < g; j++){
if (mask & (1 << j) and j != x){
suma += calcf[x][j][mid];
suma += calcb[x][j][mjesta[red[x]].size() - mid];
suma2 += calcf[x][j][mid2];
suma2 += calcb[x][j][mjesta[red[x]].size() - mid2];
}
}
if (suma < suma2) high = mid;
else low = mid2;
}
return low;
}
double rek (int mask){
if (abs(dp[mask] + 1) > 0.1) return dp[mask];
dp[mask] = 1e18;
for (int i = 0; i < g; i++){
if (mask & (1 << i)){
double tr = rek(mask - (1 << i));
int k = binary_search(i, mask - (1 << i));
double kk = k;
double suma = 0;
suma += kk * (kk - 1) / 2;
suma += (ukp[red[i]] - kk) * (ukp[red[i]] - kk - 1) / 2;
suma = suma / 2;
//cout << tr << " " << suma << endl;
for (int j = 0; j < g; j++){
if (mask & (1 << j) and j != i){
suma += calcf[i][j][k];
suma += calcb[i][j][mjesta[red[i]].size() - k];
}
}
tr += suma;
//cout << i << " " << mask << " " << k << " " << suma << " " << tr << endl;
dp[mask] = min(dp[mask], tr);
}
}
//cout << mask << " " << dp[mask] << endl;
return dp[mask];
}
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, red2[j] = g, g++;
prosli[i][j]++;
ukp[j]++;
mjesta[j].push_back(i);
}
for (int mask = 0; mask < (1 << g); mask++) dp[mask] = -1;
dp[0] = 0;
for (int g1 = 0; g1 < g; g1++){
for (int g2 = 0; g2 < g; g2++){
if (g1 != g2){
for (int i = 0; i < mjesta[red[g1]].size(); i++){
int pos = mjesta[red[g1]][i];
calcf[g1][g2][i + 1] = calcf[g1][g2][i] + prosli[pos][red[g2]];
}
for (int i = mjesta[red[g1]].size() - 1; i >= 0; i--){
int pos = mjesta[red[g1]][i];
calcb[g1][g2][mjesta[red[g1]].size() - i] = calcb[g1][g2][mjesta[red[g1]].size() - i - 1] + ukp[red[g2]] - prosli[pos][red[g2]];
//cout << g1 << " " << g2 << " " << mjesta[red[g1]].size() - i << " " <<calcb[g1][g2][mjesta[red[g1]].size() - i] << endl;
}
}
}
}
//rek(16);
ans = rek((1 << g) - 1);
cout << fixed << setprecision(10);
cout << ans << "\n";
return 0;
}
