#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 3;
string s;
int opt_cost(int color, vector<vector<int>>& prefix, int boarded, int seats) {
int n = prefix[color].back();
int cost_fb = 0;
for(int i = 0; i < N; i++) {
if((1 << i) & boarded)
cost_fb += prefix[i].back();
}
int cost_sum_pref = 0;
for(int i = 0; i < seats; i++) {
if(s[i] - 65 == color) {
for(int j = 0; j < N; j++) {
if((1 << j) & boarded) cost_sum_pref += prefix[j][i];
}
}
}
int cost_pref = 0;
int visited = 0;
int cost = n * (n - 1) / 2 + cost_sum_pref;
for(int i = 0; i < seats; i++) {
if(s[i] - 65 == color) {
visited++;
for(int j = 0; j < N; j++) {
if((1 << j) & boarded) cost_pref += prefix[j][i];
}
int newcost = visited * (visited - 1) / 2;
newcost += (n - visited) * (n - visited - 1) / 2;
//newcost += cost_pref + cost_fb * (n - visited) - (cost_sum_pref - cost_pref);
//newcost += cost_pref + cost_fb * (n - visited) - (cost_sum_pref - cost_pref);
//cout << "\t\t" << "\n";
cost = min(cost, newcost);
}
}
//cout << "\t" << cost << "\n";
return cost;
}
int32_t main() {
cin >> s;
vector<vector<int>> prefix(N, vector<int>(s.size(), 0));
for(int i = 0; i < s.size(); i++) {
prefix[s[i] - 65][i] = 1;
}
for(int i = 0; i < N; i++) {
for(int j = 1; j < s.size(); j++) {
prefix[i][j] += prefix[i][j-1];
}
}
vector<int> state(1 << N, 0x7fffffffffffffff);
vector<int> currentstates;
state[0] = 0;
currentstates.push_back(0);
while(!currentstates.empty()) {
//cout << "->\n";
vector<int> newcurrentstates;
for(int st : currentstates) {
//cout << st << ":\n";
for(int b = 0; b < N; b++) {
if((1 << b) & st) continue;
if((1 << b) > st) newcurrentstates.push_back(st | (1 << b));
int cost = opt_cost(b, prefix, st, s.size());
int newstate = (1 << b) | st;
//cout << state[st] + cost << "\n";
state[newstate] = min(state[newstate], state[st] + cost);
}
}
currentstates = newcurrentstates;
}
cout << state.back() / 2;
if(state.back() & 1) cout << ".5";
return 0;
}
