import itertools def generate_v(n): if n == 0: return [frozenset()] prev_v = generate_v(n-1) subsets = [] for r in range(len(prev_v)+1): for subset in itertools.combinations(prev_v, r): subsets.append(frozenset(subset)) return subsets def main(): N = int(input()) A = list(map(int, input().split())) A0, A1, A2, A3, A4, A5 = A if N == 0 or N == 1: print("NO") return vn = generate_v(N) ma0_idx = A0 ma1_idx = A1 ma2_idx = A2 ma3_idx = A3 ma4_idx = A4 ma5_idx = A5 for m0 in vn: for m1 in vn: for m2 in vn: ma0 = [m0, m1, m2][ma0_idx] ma1 = [m0, m1, m2][ma1_idx] valid = True for x3 in vn: if x3 in ma0 and x3 not in ma1: valid = False break if not valid: continue ma2 = [m0, m1, m2][ma2_idx] if ma1 not in ma2: continue ma3 = [m0, m1, m2][ma3_idx] if ma3 not in ma2: continue ma4 = [m0, m1, m2][ma4_idx] if ma4 not in ma2: continue ma5 = [m0, m1, m2][ma5_idx] if ma5 not in ma0: continue print("YES") return print("NO") if __name__ == "__main__": main()