#include <bits/stdc++.h>
using namespace std;
int n, g;
string s;
long double get(long double x) {
return x * (x-1)/4;
}
long double pref[100100];
long double suf[100100];
long double dp[1<<16];
vector<int> pos[1111];
long double C[100100][16][16];
int cnt[100100][16];
long double get(int mask, int d, int x) {
long double ans = 0;
for(int i = 0; i < g; i++) {
if(mask & (1<<i)) {
ans += C[d][x][i];
}
}
long double cc = cnt[d][x];
long double ALL = cnt[n][x];
return ans + get(cc) + get(ALL-cc);
}
long double calc(int mask, int x) {
if(pos[x].size() == 1) return 0;
int l = 0, r = pos[x].size() - 1;
while(l + 3 < r) {
int mid = (l + r)/2;
if(get(mask, pos[x][mid], x) < get(mask, pos[x][mid+1], x)) {
r = mid;
} else {
l = mid;
}
}
long double ans = 1e18;
for(int i = l; i <= r; i++) {
ans = min(ans, get(mask, pos[x][i], x));
}
return ans;
}
void precalc(int x, int y) {
int A = 0;
int X = 0;
for(int i = 0; i < n; i++) {
pref[i+1] = pref[i];
if(s[i] == 'A' + x) {
pref[i+1] += A;
X++;
} else if(s[i] == 'A'+y) {
A++;
}
}
X = 0;
A = 0;
for(int i = n-1; i >= 0; i--) {
suf[i] = suf[i+1];
if(s[i] == 'A' + x) {
suf[i] += A;
X++;
} else if(s[i] == 'A' + y){
A++;
}
}
for(int i = 0; i <= n; i++) {
C[i][x][y] = pref[i] + suf[i];
}
}
int main() {
cin >> s;
n = s.size();
for(int i = 0; i < 16; i++) {
pos[i].push_back(0);
}
for(int i = 0; i < n; i++) {
g = max(s[i] - 'A' + 1, g);
pos[s[i] - 'A'].push_back(i + 1);
}
for(int c = 0; c < g; c++) {
for(int i = 1; i <= n; i++) {
cnt[i][c] = cnt[i-1][c] + (s[i-1] - 'A' == c);
}
}
for(int i = 0; i < g; i++) {
for(int j = 0; j < g; j++) {
if(i == j) continue;
precalc(i, j);
}
}
for(int i = 0; i < (1<<g); i++) {
dp[i] = 1e18;
}
dp[0] = 0;
for(int mask = 0; mask < (1<<g); mask++) {
for(int i = 0; i < g; i++) {
int nmask = mask | (1<<i);
if(nmask != mask) {
dp[nmask] = min(dp[mask] + calc(mask, i), dp[nmask]);
}
}
}
cout << fixed << setprecision(12) << dp[(1<<g)-1] << "\n";
}
