#include <bits/stdc++.h>
#ifndef _DEBUG
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#endif
using namespace std;
signed main()
{
cin.tie(0);
ios_base::sync_with_stdio(false);
string s;
cin >> s;
int n = s.size();
int g = *max_element(s.begin(), s.end()) - 'A' + 1;
vector<int> a(n);
vector<vector<int>> pos(g);
for (int i = 0; i < n; i++)
pos[a[i] = s[i] - 'A'].push_back(i);
vector<vector<int>> prefix(1 << g, vector<int>(n));
vector<vector<int>> suffix(1 << g, vector<int>(n));
for (int k = 0; k < 1 << g; k++)
{
for (int i = 1; i < n; i++)
prefix[k][i] = prefix[k][i - 1] + bool(1 << a[i - 1] & k);
for (int i = n - 2; i >= 0; i--)
suffix[k][i] = suffix[k][i + 1] + bool(1 << a[i + 1] & k);
}
vector<double> dp(1 << g, 1e20);
dp[0] = 0;
for (int b = 1; b < 1 << g; b++)
{
for (int i = 0; i < g; i++)
{
if (!(b & (1 << i)))
continue;
double cost = 0;
for (int p : pos[i])
{
cost += min(prefix[b][p] - 0.5 * prefix[(1 << i)][p], suffix[b][p] - 0.5 * suffix[(1 << i)][p]);
}
dp[b] = min(dp[b], dp[b ^ (1 << i)] + cost);
}
}
cout << setprecision(15) << dp.back();
}
