/** 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


bool ok(int x, const string& s)
{
	int n=sz(s);
	vector<int> C(1<<3,0);
	ll SC=0;
	FOR(i,0,n)
	{
		int t=s[i]-'A';
		bool ok=false;
		FOR(mask,1,(1<<3)-1)
		{
			if(__popcount(mask)==2 && C[mask]!=0)
			{
				if(!((mask>>t)&1))
				{
					SC -= 1;
					C[mask]-=1;
					ok=true;
					break;
				}
			}
		}
		if(!ok)
		{
			FOR(mask,1,(1<<3)-1)
			{
				if(__popcount(mask)==1 && C[mask]!=0)
				{
					if(!((mask>>t)&1))
					{
						C[mask]-=1;
						ok=true;
						C[mask|(1<<t)] += 1;
						break;
					}
				}
			}
		}
		if(!ok)
		{
			++SC;
			C[1<<t]+=1;
		}
		if(SC > x) return false;
	}
	return true;
}

int solve()
{
	string s;
	if(!(cin>>s))return 1;
	
	int l=0, r=sz(s)/3;
	while(r-l>1)
	{
		int mid=(l+r)/2;
		if(ok(mid,s))
			r=mid;
		else
			l=mid;
	}
		
	cout<<r<<'\n';
    return 0;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int TET = 1e9;
    //cin >> TET;
    for (int i = 1; i <= TET; i++)
    {
        if (solve())
        {
            break;
        }
#ifdef ONPC
        cout << "__________________________" << endl;
#endif
    }
#ifdef ONPC
    cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
#endif
}