#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
	int N, K;
	cin >> N >> K;
	vector<int> A(N), B(N), perm(N);
	for (int i = 0; i < N; ++i) {
		cin >> A[i] >> B[i];
		perm[i] = i;
	}
	sort(perm.begin(), perm.end(), [&](int i, int j) { return A[i] - B[i] > A[j] - B[j]; });
	string ans(N, 'B');
	for (int i = 0; i < K; ++i) {
		ans[perm[i]] = 'A';
	}
	cout << ans << endl;
	return 0;
}