#include<bits/stdc++.h>
using namespace std;
#include <unordered_set>
#include <random>
//#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=MOD;
const ll MAX=200010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;



void solve(){
    int N;
    cin>>N;
    vector<long long>A(N);
    rep(i,N)cin>>A[i];
    int ans=2;
    int s[]={261,294,327,348,392,436,490};
    ll mi=INF;
    rep(i,7){
        ll ma=0;
        rep(j,N){
            if(j+(N/s[i])+1<N){
                ll x=A[j+N/s[i]];
                x+=A[j+N/s[i]+1];
                x+=A[j+N/s[i]-1];
                ma=max(ma,abs(x/3-A[j]));
            }
        }
        if(ma<mi){
            ans=(i+2)%7;
            mi=ma;
        }
        //cout<<ma<<endl;
    }
    cout<<(char)('A'+ans)<<4<<endl;
}

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}