#include<iostream>
using namespace std;
int N;
string S;
int LA[2<<17],RC[2<<17];
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin>>N>>S;
	long long base=0;
	int hatena=0;
	long long add=0;
	for(int i=0;i<N;i++)
	{
		LA[i+1]=LA[i];
		if(S[i]=='A')
		{
			LA[i+1]++;
		}
		else if(S[i]=='C')
		{
			base+=LA[i];
		}
		else
		{
			hatena++;
			add+=LA[i];
		}
	}
	for(int i=N;i--;)
	{
		RC[i]=RC[i+1];
		if(S[i]=='C')RC[i]++;
	}
	long long plus=add;
	int vis=0;
	for(int i=0;i<N;i++)if(S[i]=='?')
	{
		plus-=LA[i];
		plus+=RC[i];
		vis++;
		add=max(add,plus+(long long)vis*(hatena-vis));
	}
	cout<<base+add<<endl;
}