//1文字ずつ確定させていく
#include <iostream>
#include <string>
using namespace std;

int n, d;

int main() {
	cin >> n >> d;
	
	int rem_holl = d;
	string ans;
	for (int i = 1; i <= n; i++) {
		if (0 <= rem_holl - 1 && rem_holl - 1 <= 2 * (n - i)) { ans += 'A'; rem_holl -= 1; continue; }	//残りn-i文字で穴の個数をrem_holl - 1個にできればAを選択
		if (0 <= rem_holl - 2 && rem_holl - 2 <= 2 * (n - i)) { ans += 'B'; rem_holl -= 2; continue; }
		if (0 <= rem_holl &&     rem_holl     <= 2 * (n - i)) { ans += 'C'; continue; }
	}
	cout << ans << endl;
	return 0;
}