#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define PA pair<ll,ll>
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) (UB(A,x)-LB(A,x))
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
using mint=modint1000000007;
//using mint=modint998244353;
void chmax(ll&a,ll b){a=max(a,b);}
void chmin(ll&a,ll b){a=min(a,b);}
void print(vector<ll>A){REP(i,A.size()){if(i)cout<<" ";cout<<A[i];}cout<<endl;}
ld dist(ld x1,ld y1,ld x2,ld y2){return sqrtl((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}
int main(){
  ll N;cin>>N;
  vector<ll>A(N);
  REP(i,N)cin>>A[i];
  string S="CDEFGAB";
  vector<ld>F={261.6,294.3,327.0,348.8,392.4,436.0,490.5};
  ll ans=0,score=1e18;
  REP(i,7){
    ll d=0;
    ll T=round(N/F[i]);
    REP(i,N-T)chmax(d,abs(A[i]-A[i+T]));
    if(d<score){
      score=d;ans=i;
    }
  }
  cout<<S[ans]<<4<<endl;
  return 0;
}