#include <bits/stdc++.h>
#define REP(i,a,b) for(int i=(a);i<(b);i++)
#define RREP(i,a,b) for(int i=(a);i>=(b);i--)
typedef long long ll; typedef long double ld;
using namespace std;
const int INF=1e9, MOD=1e9+7, around[]={0,1,1,-1,-1,0,-1,1,0,0};
const ld PI=abs(acos(-1));
int n,pos;
ll a;

int main(){
	cin >> n;
	REP(i,0,n){
		cin >> a;
		if(!i) pos=a;
		if(a<4) pos^=a;
		else{
			cout << 'B' << endl;
			return 0;
		}
	}
	
	cout << (pos?'A':'B') << endl;
	return 0;
}