#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}

//https://ei1333.github.io/library/other/xor-shift.cpp.html
struct XorShift {
private:
    constexpr static double R = 1.0 / 0xffffffff;
    uint64_t x;

public:
    explicit XorShift(uint64_t seed = 88172645463325252ull) : x(seed) {}

    template< typename T = uint64_t >
    inline T get() { // [0, 2^64)
        x ^= x << 7ull;
        x ^= x >> 9ull;
        return x;
    }

    inline uint32_t get(uint32_t r) { // [0, r)
        return ((uint64_t) get< uint32_t >() * r) >> 32ull;
    }

    inline uint32_t get(uint32_t l, uint32_t r) { // [l, r)
        return l + get(r - l);
    }

    inline double probability() { // [0.0, 1.0]
        return get< uint32_t >() * R;
    }
};


template<class T>
void shuffle_vector(vector<T> &p,XorShift &table){
    int L=p.size();
    for(int i=0;i<L;i++){
        int ind=table.get(i,L);
        swap(p[ind],p[i]);
    }
    return ;
}

const int n = 10000;

vector<ll> make(int seed = 0){
    vector<ll> res(n);
    XorShift table(seed);
    rep(i, 0, n) res[i] = table.get() % 1'000'000'000'000ll + 1;
    return res;
}


vector<vector<int>> f(vector<ll> A){
    const int M = 1665;
    vector<vector<pair<int, int>>> p(6);
    rep(i, 0, 6){
        rep(j, 0, M) rep(k, j + 1, M){
            p[i].push_back({j + i * M, k + i * M});
        }
        sort(all(p[i]), [&](pair<int, int> l, pair<int, int> r){
            return A[l.first] + A[l.second] < A[r.first] + A[r.second];
        });
    }
    int L = M * (M - 1) / 2;
    auto calc = [&](pair<int, int> a) -> ll {
        return A[a.first] + A[a.second];
    };
    auto ch = [&](ll m, vector<pair<int, int>> &l, vector<pair<int, int>> &r) -> vector<int> {
        int ind = L - 1;
        rep(i, 0, L){
            while (ind != -1){
                if (calc(l[i]) + calc(r[ind]) == m){
                    return {l[i].first, l[i].second, r[ind].first, r[ind].second};
                }
                else if (calc(l[i]) + calc(r[ind]) > m) ind--;
                else break;
            }
        }
        return {};
    };
    XorShift table;
    rep(rp, 0, 100){
        int a = table.get() % L;
        int b = table.get() % L;
        ll sum = calc(p[0][a]) + calc(p[1][b]);
        auto tmp0 = ch(sum, p[0], p[1]);
        assert(!tmp0.empty());
        auto tmp1 = ch(sum, p[2], p[3]);
        auto tmp2 = ch(sum, p[4], p[5]);
        if (tmp1.empty() || tmp2.empty()) continue;
        return {tmp0, tmp1, tmp2};
    }
    return {};
}

void solve();
// CITRUS CURIO CITY / FREDERIC
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    int N;
    cin >> N;
    if (N == 6){
        cout << "ABC.BA\n";
    }
    else{
        vector<ll> A(N);
        rep(i, 0, N) cin >> A[i];
        auto ans = f(A);
        assert(!ans.empty());
        string S;
        rep(i, 0, N) S += ".";
        rep(i, 0, 3) for (auto x : ans[i]){
            S[x] = (char)('A' + i);
        }
        cout << S << "\n";
    }
}