#include <bits/stdc++.h>
#define MP make_pair
#define PB push_back
#define int long long
#define st first
#define nd second
#define rd third
#define FOR(i, a, b) for(int i =(a); i <=(b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REP(i, n) for(int i = 0;i <(n); ++i)
#define VAR(v, i) __typeof(i) v=(i)
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define __builtin_ctz __builtin_ctzll
#define __builtin_clz __builtin_clzll
#define __builtin_popcount __builtin_popcountll
using namespace std;
template<typename TH> void _dbg(const char* sdbg, TH h) { cerr<<sdbg<<"="<<h<<"\n"; }
template<typename TH, typename... TA> void _dbg(const char* sdbg, TH h, TA... t) {
  while(*sdbg != ',') { cerr<<*sdbg++; } cerr<<"="<<h<<","; _dbg(sdbg+1, t...);
}
#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define debugv(x) {{cerr <<#x <<" = "; FORE(itt, (x)) cerr <<*itt <<", "; cerr <<"\n"; }}
#else
#define debug(...) (__VA_ARGS__)
#define debugv(x)
#define cerr if(0)cout
#endif
#define left ____left
#define hash ____hash
typedef long long ll;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VLL;
typedef vector<pair<int, int> > VPII;
typedef vector<pair<ll, ll> > VPLL;

template<class C> void mini(C&a4, C b4){a4=min(a4, b4); }
template<class C> void maxi(C&a4, C b4){a4=max(a4, b4); }
template<class T1, class T2>
ostream& operator<< (ostream &out, pair<T1, T2> pair) { return out << "(" << pair.first << ", " << pair.second << ")";}
template<class A, class B, class C> struct Triple { A first; B second; C third;
  bool operator<(const Triple& t) const { if (st != t.st) return st < t.st; if (nd != t.nd) return nd < t.nd; return rd < t.rd; } };
template<class T> void ResizeVec(T&, vector<int>) {}
template<class T> void ResizeVec(vector<T>& vec, vector<int> sz) {
  vec.resize(sz[0]); sz.erase(sz.begin()); if (sz.empty()) { return; }
  for (T& v : vec) { ResizeVec(v, sz); }
}
typedef Triple<int, int, int> TIII;
template<class A, class B, class C>
ostream& operator<< (ostream &out, Triple<A, B, C> t) { return out << "(" << t.st << ", " << t.nd << ", " << t.rd << ")"; }
template<class T> ostream& operator<<(ostream& out, vector<T> vec) { out<<"("; for (auto& v: vec) out<<v<<", "; return out<<")"; }
template<class T> ostream& operator<<(ostream& out, set<T> vec) { out<<"("; for (auto& v: vec) out<<v<<", "; return out<<")"; }
template<class L, class R> ostream& operator<<(ostream& out, map<L, R> vec) { out<<"("; for (auto& v: vec) out<<v<<", "; return out<<")"; }

const int kInf = 1e18;
const int N = 1e6 + 5;
int a[N], b[N];
int typ[N];
int aktc, shift;
vector<int> deactivated;
int32_t main() {

  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(10);
  cerr << fixed << setprecision(10);
  cin.tie(0);
  //double beg_clock = 1.0 * clock() / CLOCKS_PER_SEC;
  
  int n, k;
  cin>>n>>k;
  RE (i, n) {
    cin>>a[i];
  }
  RE (i, n) {
    cin>>b[i];
  }
  int cnt_a = 0;
  RE (i, n) {
    if (a[i] < b[i]) {
      cnt_a++;
      typ[i] = 1;
    }
  }
  int swapped = 0;
  if (cnt_a > k) {
    cnt_a = n - cnt_a;
    k = n - k;
    RE (i, n) {
      swap(a[i], b[i]);
      typ[i] = 1 - typ[i];
    }
    swapped = 1;
  }
  debug(swapped, cnt_a, k);
  int lbd = 0;
  int bil = 0;
  RE (i, n) {
    bil += min(a[i], b[i]);
    maxi(bil, 0ll);
    maxi(lbd, bil);
  }
  int need_changed = k - cnt_a;
  int kl = lbd, kp = kInf, faj = kInf;
  string best;
  while (kl <= kp) {
    aktc = (kl + kp) / 2;
    shift = 0;
    VI bils{0};
    deactivated.clear();
    string here(n + 1, 'B');
    set<PII> active;
    int on_set = 0;
    int fail = 0;
    RE (i, n) {
      if (typ[i] == 1) { // moje tansze
        here[i] = 'A';
        shift += a[i];
      } else { // jego tansze
        shift += b[i];
        active.insert({a[i] - b[i], i});
        on_set += a[i] - b[i];
      }
      while (shift < 0) {
        if (active.empty()) {
          shift = 0;
          break;
        }
        auto it = active.begin();
        if (shift + it->st <= 0) {
          deactivated.PB(it->nd);
          shift += it->st;
          on_set -= it->st;
          active.erase(active.begin());
        } else {
          PII p2 = *it;
          p2.st += shift;
          on_set += shift;
          active.erase(active.begin());
          active.insert(p2);
          shift = 0;
        }
      }
      while (shift + on_set > aktc) {
        if (active.empty()) {
          fail = 1;
          break;
        }
        on_set -= prev(active.end())->st;
        active.erase(prev(active.end()));
      }
    }
    for (auto p : active) {
      deactivated.PB(p.nd);
    }
    if (!fail && SZ(deactivated) >= need_changed) {
      faj = aktc;
      kp = aktc - 1;
      REP (i, need_changed) {
        here[deactivated[i]] = 'A';
      }
      best = here;
    } else {
      kl = aktc + 1;
    }
  }
  cout<<faj<<endl;
  if (swapped) {
    RE (i, n) {
      best[i] = ((best[i] + 1) ^ 1) - 1;
      swap(a[i], b[i]);
    }
    k = n - k;
  }
  cout<<best.substr(1)<<"\n";
#ifdef LOCAL
  lbd = 0;
  bil = 0;
  int cnta = 0;
  RE (i, n) {
    if (best[i] == 'A') {
      bil += a[i];
      cnta++;
    } else {
      bil += b[i];
    }
    maxi(bil, 0ll);
    maxi(lbd, bil);
  }
  assert(cnta == k);
  assert(lbd == faj);
#endif
  
  return 0;
}