#include <bits/stdc++.h>
using namespace std;
#define For(Ti,Ta,Tb) for(auto Ti=(Ta);Ti<=(Tb);++Ti)
#define Dec(Ti,Ta,Tb) for(auto Ti=(Ta);Ti>=(Tb);--Ti)
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define range(Tx) begin(Tx),end(Tx)
using ll=long long;
const int N=3e5+5;
int n,k,a[N],b[N],ans[N],ban[N];
string sym("AB");
bool check(ll mid){
	For(i,1,n) ans[i]=ban[i];
	set<pair<int,int>> st;
	ll s1=0,s2=0;
	vector<int> vec;
	For(i,1,n){
		s1+=a[i];
		if(!ban[i]){
			s2+=b[i]-a[i];
			st.emplace(b[i]-a[i],i);
		}
		while(s1+s2>mid){
			if(!st.size()) return 0;
			auto it=prev(st.end());
			s2-=it->first;
			st.erase(it);
		}
		while(s1<0){
			if(!st.size()){
				s1=0;
				break;
			}
			auto [x,id]=*st.begin();
			st.erase(st.begin());
			s2-=x;
			if(s1+x<0){
				s1+=x;
				vec.push_back(id);
			}else{
				st.emplace(x+s1,id);
				s2+=x+s1;
				s1=0;
			}
		}
	}
	for(auto [x,id]:st){
		vec.push_back(id);
	}
	if(int(vec.size())<k) return 0;
	For(i,0,k-1) ans[vec[i]]=1;
	return 1;
}
int main(){
	cin.tie(nullptr)->sync_with_stdio(false);
	cin>>n>>k;
	k=n-k;
	For(i,1,n) cin>>a[i];
	For(i,1,n) cin>>b[i];
	int cnt=0;
	For(i,1,n) cnt+=(a[i]>b[i]);
	if(cnt>k){
		sym="BA";
		For(i,1,n) swap(a[i],b[i]);
		k=n-k;
	}
	For(i,1,n){
		if(a[i]>b[i]){
			ban[i]=1;
			swap(a[i],b[i]);
			--k;
		}
	}
	ll l=0,r=1e14;
	while(l<r){
		ll mid=(l+r)/2;
		if(check(mid)) r=mid;
		else l=mid+1;
	}
	assert(check(l));
	cout<<l<<'\n';
	For(i,1,n) cout<<sym[ans[i]];
	cout<<'\n';
	return 0;
}