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#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>

using namespace __gnu_pbds;
using namespace std;


typedef tree<
    pair<long long, int>,
    null_type,
    less <pair<long long, int>>,
    rb_tree_tag,
    tree_order_statistics_node_update
> ordered_set;


const int MAXV = 1000 * 1000 * 1000;


pair <bool, vector<int>> check(int n, int k, long long x, vector <int> &a, vector <int> &b, bool trackSol) {
    int l = 0, r = 0;
    long long dpL = 0, dpR = 0, dpMin = 0;

    vector <int> ansHints;
    ordered_set diffNeg, diffPos;

    int timestamp = 0;
    for (int i = 0; i < n; i++) {
        r++;

        dpL += b[i];
        dpR += a[i];
        dpMin += min(a[i], b[i]);

        if (dpMin > x) {
            return {false, {}};
        }

        long long abDiff = a[i] - b[i];
        if (abDiff < 0) {
            diffNeg.insert({abDiff, timestamp++});
        } else if (abDiff > 0) {
            diffPos.insert({abDiff, timestamp++});
        }

        if (trackSol) {
            int idx;
            if (abDiff < 0) {
                idx = l + diffNeg.order_of_key({abDiff, -1});
            } else if (abDiff > 0) {
                idx = r - (diffPos.size() - diffPos.order_of_key({abDiff, -1}));
            } else {
                idx = l + diffNeg.size();
            }

            ansHints.push_back(idx);
        }

        if (dpMin < 0) {
            long long dpCurrLeft = dpMin, dpCurrRight = dpMin;

            while (!diffNeg.empty() && dpCurrLeft <= 0) {
                auto it = prev(diffNeg.end());
                dpCurrLeft -= it->first;
                diffNeg.erase(it);
            }

            while (!diffPos.empty() && dpCurrRight <= 0) {
                auto it = diffPos.begin();
                dpCurrRight += it->first;
                diffPos.erase(it);
            }

            if (dpCurrLeft > 0) diffNeg.insert({-dpCurrLeft, timestamp++});
            if (dpCurrRight > 0) diffPos.insert({dpCurrRight, timestamp++});

            dpMin = 0;
            dpL = max(dpL, 0LL);
            dpR = max(dpR, 0LL);
        }

        while (dpL > x) {
            dpL += diffNeg.begin()->first;
            diffNeg.erase(diffNeg.begin());
            l++;
        }

        while (dpR > x) {
            auto it = prev(diffPos.end());
            dpR -= it->first;
            diffPos.erase(it);
            r--;
        }
    }

    return {l <= k && k <= r, ansHints};
}

string recover(int n, int k, vector <int> &ansHints) {
    string ans(n, 'B');
    for (int i = n - 1; i >= 0; i--) {
        if (k > ansHints[i]) {
            ans[i] = 'A';
            k--;
        }
    }

    return ans;
}

pair <long long, string> solve(int n, int k, vector <int> &a, vector <int> &b) {
    long long l = -1, r = (long long) n * MAXV;
    while (r - l > 1) {
        long long mid = (l + r) / 2;
        if (check(n, k, mid, a, b, false).first) {
            r = mid;
        } else {
            l = mid;
        }
    }

    auto ansHints = check(n, k, r, a, b, true).second;
    return {r, recover(n, k, ansHints)};
}

int main() {
    ios_base::sync_with_stdio(false);

    int n, k;
    cin >> n >> k;

    vector <int> a(n), b(n);
    for (int &ai : a) cin >> ai;
    for (int &bi : b) cin >> bi;

    auto [cost, sol] = solve(n, k, a, b);
    cout << cost << '\n' << sol << endl;

    return 0;
}