/** gnu specific **/
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
/** contains everything I need in std **/
#include <bits/stdc++.h>

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(S) ((int)S.size())
#define FOR(i, st_, n) for(int i = st_; i < n; ++i)
#define RFOR(i, n, end_) for(int i = (n)-1; i >= end_; --i)
#define x first
#define y second
#define pb push_back
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ull, ull> pull;
using namespace __gnu_pbds;
typedef tree<ll, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
using namespace std;
#ifdef ONPC
mt19937 rnd(228);
#else
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
#endif


int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    string s;
    cin >> s;
    vector<pll> ar;
    vector<ll> a;
    vector<ll> b;
    vector<ll> c;
    ll n = sz(s);
    FOR(i,0,n)
    {
        if(s[i] == 'A')
            a.pb(i);
        else if(s[i] == 'B')
            b.pb(i);
        else
            c.pb(i);
    }
    FOR(i,0,n/3)
    {
        ar.pb({min(a[i],min(b[i],c[i])),max(a[i],max(b[i],c[i]))});
    }
    sort(all(ar));
    priority_queue<ll> res;
    res.push(-1*ar[0].y);
    FOR(i,1,n/3)
    {
        if(ar[i].x > (-res.top()))
        {
            res.pop();
            res.push(-1*ar[i].y);
        }
        else
        {
            res.push(-1*ar[i].y);
        }
    }
    cout << sz(res);
}