def main():
    N, M = map(int, input().split())
    T = {tuple(map(int, input().split())) for _ in [0] * M}

    if M == 1:
        print('YES')
        exit()

    station = [0] * N
    for a, b in T:
        station[a] += 1
        station[b] += 1

    cnt = tuple(filter(lambda n:n==2, station))
    if len(cnt) == M - 1:
        print('YES')
    else:
        print('NO')

main()