#include <stdio.h>
#include <stdlib.h>

long double solve(int N, int A[], long double f)
{
	int i, l, r;
	long double w = 44100 / f, ans = 0.0;
	for (i = 1; i <= N; i++) {
		l = i + (int)w;
		r = l + 1;
		if (r >= N) break;
		ans += fabsl(A[i] - (A[l] * (1.0 - (w - (int)w)) + A[r] * (w - (int)w)));
	}
	return ans;
}

int main()
{
	int i, N, A[44101];
	scanf("%d", &N);
	for (i = 1; i <= N; i++) scanf("%d", &(A[i]));
	
	long double min = 1e+10, tmp;
	char ans = 0;
	tmp = solve(N, A, 261.6);
	if (min > tmp) {
		min = tmp;
		ans = 'C';
	}
	tmp = solve(N, A, 294.3);
	if (min > tmp) {
		min = tmp;
		ans = 'D';
	}
	tmp = solve(N, A, 327.0);
	if (min > tmp) {
		min = tmp;
		ans = 'E';
	}
	tmp = solve(N, A, 348.8);
	if (min > tmp) {
		min = tmp;
		ans = 'F';
	}
	tmp = solve(N, A, 392.4);
	if (min > tmp) {
		min = tmp;
		ans = 'G';
	}
	tmp = solve(N, A, 436.0);
	if (min > tmp) {
		min = tmp;
		ans = 'A';
	}
	tmp = solve(N, A, 490.5);
	if (min > tmp) {
		min = tmp;
		ans = 'B';
	}
	printf("%c4\n", ans);
	fflush(stdout);
	return 0;
}