#include<bits/stdc++.h> 
using namespace std;

stack<int> st;//stl栈；
int n, in = 1;
int main(){
   cin>>n;
    while (n--){
         int x;  cin>>x;
         if (in > x) st.pop();
         else
             while(in<=x)
             {
                 st.push(in);
                 putchar('A');
                 in++;
             }
         putchar('B');
    }
   putchar('\n');
    return 0;
}


/**************************************************************
	Problem: 1791
	User: admin
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2076 kb
****************************************************************/