#include <bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
#define endl '\n'
#define int ll
#define ld long double
using namespace std;
const ld INF = 1e18;
const ld eps = 1e-9;
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
string s;
cin >> s;
int N = s.size();
vector<int> arr(N), mapa(26, 0);
vector<int> conv;
for (int i = 0; i < N; i++)
{
arr[i] = s[i] - 'A';
conv.push_back(arr[i]);
}
sort(conv.begin(), conv.end());
conv.erase(unique(conv.begin(), conv.end()), conv.end());
for (int i = 0; i < conv.size(); i++)
mapa[conv[i]] = i;
int G = conv.size();
vector<vector<int>> pf(N + 1, vector<int>(G, 0));
for (int i = 0; i < N; i++)
{
arr[i] = mapa[arr[i]];
pf[i + 1][arr[i]]++;
for (int j = 0; j < G; j++)
pf[i + 1][j] += pf[i][j];
}
vector<vector<vector<int>>> L(N, vector<vector<int>>(G, vector<int>(G, 0)));
vector<vector<vector<int>>> R(N, vector<vector<int>>(G, vector<int>(G, 0)));
for (int j = 0; j < G; j++)
for (int k = 0; k < G; k++)
{
int cn = 0;
for (int i = 0; i < N; i++)
{
if (j == k)
{
L[i][j][k] = 0;
continue;
}
if (i - 1 >= 0)
L[i][j][k] += L[i - 1][j][k];
if (arr[i] == k)
++cn;
else if (arr[i] == j)
L[i][j][k] += cn;
}
cn = 0;
for (int i = N - 1; i >= 0; i--)
{
if (j == k)
{
R[i][j][k] = 0;
continue;
}
if (i + 1 < N)
R[i][j][k] += R[i + 1][j][k];
if (arr[i] == k)
++cn;
else if (arr[i] == j)
R[i][j][k] += cn;
}
}
auto f = [&](int idx, int g, int bit)
{
int req_passes = 0;
for (int j = 0; j < G; j++)
if (bit & (1LL << j))
{
if (idx + 1 < N)
req_passes += L[idx][g][j] + R[idx + 1][g][j];
else
req_passes += L[idx][g][j];
}
int lava_cnt = pf[idx + 1][g];
int prava_cnt = pf[N][g] - lava_cnt;
ld ret = (lava_cnt * (lava_cnt - 1) * 1.0L) + (prava_cnt * (prava_cnt - 1) * 1.0L);
ret *= 0.25L;
ret += req_passes * 1.0L;
return ret;
};
auto ternary_search = [&](int g, int bit)
{
int l = 0, r = N - 1;
while ((r - l) > 3)
{
int tret = (r - l) / 3;
int lm = l + tret, rm = r - tret;
ld vll = f(lm, g, bit), vlr = f(rm, g, bit);
if (abs(vlr - vll) < eps)
{
l = lm;
r = rm;
}
else if ((vlr - vll) > eps)
r = rm;
else
l = lm;
}
ld mn = f(l, g, bit);
for (int i = l + 1; i <= r; i++)
mn = min(mn, f(i, g, bit));
return mn;
};
vector<ld> dp(1LL << G, INF);
dp[0] = 0;
for (int bit = 0; bit < (1LL << G); bit++)
{
for (int j = 0; j < G; j++)
{
if (bit & (1LL << j))
continue;
dp[bit | (1LL << j)] = min(dp[bit | (1LL << j)], dp[bit] + ternary_search(j, bit));
}
}
cout << setprecision(9) << dp[(1LL << G) - 1] << endl;
}
