#include <bits/stdc++.h>
using namespace std;
typedef long double ld;
typedef long long ll;
string s; int n;
vector <int> pos[26];
int val[100001][26];
int val2[100001][26];
ld dp[(1 << 15)];
vector <int> dd;
int cnt;
ld ans (int mask) {
ld &ret = dp[mask];
if (ret == ret) return ret;
ret = 1e18;
if (mask == (1 << cnt) - 1) return ret = 0;
for (int i = 0; i < cnt; i++) {
if (mask & (1 << i)) continue;
int m = pos[dd[i]].size();
ld sum = 0;
for (int j = 0; j < m; j++) {
int ret1 = 0, ret2 = 0;
for (int k = 0; k < cnt; k++) {
if (mask & (1 << k)) {
ret1 += val[pos[dd[i]][j]][dd[k]];
ret2 += val2[pos[dd[i]][j]][dd[k]];
}
}
sum += min(ret1 + j * 0.5, ret2 + (m - j - 1) * 0.5);
}
ret = min(ret, sum + ans(mask ^ (1 << i)));
}
return ret;
}
int main () {
memset(dp, -1, sizeof(dp));
cin >> s; n = s.length();
for (int i = 0; i < n; i++) {
pos[s[i] - 'A'].push_back(i);
}
int x = 0;
for (int i = 1; i < 26; i++) if (!pos[i].empty()) x = i;
for (int i = 0; i <= x; i++) if (!pos[i].empty()) dd.push_back(i);
cnt = dd.size();
for (int i = 0; i < n; i++) {
for (int j = 0; j < 26; j++) {
if (pos[j].empty()) continue;
if (s[i] - 'A' == j) continue;
int l = 0, r = (int)pos[j].size() - 1, ans = 0;
while (l <= r) {
int m = (l + r) >> 1;
if (pos[j][m] < i) {
l = m + 1; ans = m + 1;
} else {
r = m - 1;
}
}
val[i][j] = ans; val2[i][j] = (int)pos[j].size() - ans;
}
}
cout << fixed << setprecision(6) << ans(0) << '\n';
}
