#include<bits/stdc++.h>
using namespace std;
constexpr int Inf = 2000000000;
constexpr long long INF= 2000000000000000000;

template<typename T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<typename T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }

template<typename T,typename U>
T modpow(T N, U P, T M = -1) {
    if(P < 0) return 0;
    T ret = 1;
    if(M != -1) ret %= M;
    while(P) {
        if(P & 1) {
            if(M == -1) ret *= N;
            else ret = ret * N % M;
        }
        P /= 2;
        if(M == -1) N *= N;
        else N = N * N % M;
    }
    return ret;
}

constexpr long long MOD = 998244353;

int main() {
    int n;
    cin >> n;
    vector<long long> vec(n);
    for(auto& x: vec) cin >> x;
    vector<int> period = {169,150,135,126,112,101,90};
    int ret = -1;
    long long ret_num = INF;
    for(int i = 0;i < 7;i++) {
        long long diff = 0;
        for(int j = 0;j < n;j++) {
            diff += (vec[j] - vec[(j + period[i]) % n]) * (vec[j] - vec[(j + period[i]) % n]);
        }
        if(ret_num > diff) {
            ret = i;
            ret_num = diff;
        }
    }

    switch(ret) {
        case 0:
            cout << "C4" << endl;
            break;
        case 1:
            cout << "D4" << endl;
            break;
        case 2:
            cout << "E4" << endl;
            break;
        case 3:
            cout << "F4" << endl;
            break;
        case 4:
            cout << "G4" << endl;
            break;
        case 5:
            cout << "A4" << endl;
            break;
        case 6:
            cout << "B4" << endl;
            break;

        default:
            assert(-1);
    }
}