#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define INF 1000000000
#define MOD 998244353
#define MAX 1000

int main(){
  int N;
  cin>>N;
  vector<int> A(N);
  for(int i=0;i<N;i++){
    cin>>A[i];
  }
  vector<double> f(7);
  f[0]=261.6;
  f[1]=294.3;
  f[2]=327.0;
  f[3]=348.8;
  f[4]=392.4;
  f[5]=436.0;
  f[6]=490.5;
  vector<string> ans(7);
  ans[0]="C4";
  ans[1]="D4";
  ans[2]="E4";
  ans[3]="F4";
  ans[4]="G4";
  ans[5]="A4";
  ans[6]="B4";

  vector<double> chi(7,0.0);
  for(int i=0;i<7;i++){
    int w=(double)N/f[i];
    for(int j=0;j<40000;j++){
      chi[i]+=pow(A[j+w]-A[j],2.0);
    }
  }

  int k=0;
  for(int i=0;i<7;i++){
    if(chi[k]>chi[i]){
      k=i;
    }
  }
  cout<<ans[k]<<'\n';
}