#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 10000000000000000

int main(){
	
	int N,K;
	cin>>N>>K;
	
	vector<pair<long long,int>> v(N);
	rep(i,N){
		long long a,b;cin>>a>>b;
		v[i] = make_pair(a-b,i);
	}
	sort(v.rbegin(),v.rend());
	
	string ans(N,'B');
	rep(i,K){
		ans[v[i].second] = 'A';
	}
	cout<<ans<<endl;
	
	
	return 0;
}