#include <bits/stdc++.h>
// #include <atcoder/all>
using namespace std;
// using namespace atcoder;
typedef int64_t lint;
#define rep(i, n) for(int i=0; i<n; i++)
#define repx(i, l, n) for(int i=l; i<n; i++)
#define all(v) v.begin(), v.end()
#define show(x) cout << #x << ": " << x << endl;
#define list(x) cout << #x << ": " << x << "  ";
#define pb push_back
using vi = vector<lint>;
using vvi = vector<vector<lint>>;
template<class T> inline void vin(vector<T>& v) { rep(i, v.size()) cin >> v.at(i); }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T> inline void drop(T x) { cout << x << endl; exit(0); }
template<class T> void vout(vector<T> v) { rep(i, v.size()) { cout << v.at(i) << ' '; } cout << endl; }
constexpr lint LINF = LLONG_MAX/2;

int main() {
	lint N;
	cin >> N;
	vi v(N);
	vin(v);

	lint a=0, b=0, c=LINF, x, y, z, ans;
	double d[7] = {261.6, 294.3, 327.0, 348.8, 392.4, 436.0, 490.5};
	rep(i, 7) {
		a = -LINF, b = LINF;
		double t = 0;
		while ((lint)t+1 < N) {
			x = (lint)t, y = (lint)t+1;
			z = (t-x)*10;
			// list(x) list(y) show(z)
			chmax(a, (v[x]*(10-z)+v[y]*z)/10);
			chmin(b, (v[x]*(10-z)+v[y]*z)/10);
			t += 44100.0/d[i];
		}
		if (chmin(c, a-b)) ans = i;
	}
	if (ans == 0) std::cout << "C4" << '\n';
	if (ans == 1) std::cout << "D4" << '\n';
	if (ans == 2) std::cout << "E4" << '\n';
	if (ans == 3) std::cout << "F4" << '\n';
	if (ans == 4) std::cout << "G4" << '\n';
	if (ans == 5) std::cout << "A4" << '\n';
	if (ans == 6) std::cout << "B4" << '\n';
}