#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<double> vd;
#define sz(x) (int)(x).size()
vi B;
vd dp;
double calc(ll k1, ll k2)
{
return (k1 * (k1 - 1) + k2 * (k2 - 1)) / (double)4;
}
double expectOneGroup(ll N)
{
ll k1 = ceil(N / (double)2), k2 = floor(N / (double)2);
return calc(k1, k2);
}
double compute(int mask, int lg) // lg is a bitvector with the bit of the group set
{
int others = mask ^ lg;
ll k1 = 0, k2 = 0; // passenger split of this Gruop lg
ll o1 = 0, o2 = 0; // other passengers l and right
ll safeOtherCost = 0;
for (int i = sz(B) - 1; i >= 0; --i)
if (B[i] == lg)
++k2, safeOtherCost += o2;
else if (B[i] & mask)
++o2;
double res = dp[others] + safeOtherCost + calc(k1, k2);
for (int i = 0; i < sz(B); ++i)
{
if (B[i] == lg)
{
++k1, --k2;
safeOtherCost = safeOtherCost - o2 + o1;
}
else if (B[i] & mask)
{
++o1, --o2;
}
res = min(res, dp[others] + safeOtherCost + calc(k1, k2));
}
return res;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
string P;
cin >> P;
ll N = sz(P);
int G = 0;
B.resize(N);
for (int i = 0; i < N; ++i)
B[i] = (1 << (P[i] - 'A')), G = max(G, P[i] - 'A');
++G; // to get the size
dp.assign(1 << G, calc(100100, 100100));
dp[0] = 0;
for (int i = 1; i < sz(dp); ++i)
{
for (int j = 0; j < G; ++j)
{ // last group to enter
if (((1 << j) & i) == 0)
continue;
dp[i] = min(dp[i], compute(i, (1 << j)));
}
}
// double res = expectOneGroup(N);
printf("%f\n", dp[(1 << G) - 1]);
return 0;
}
