from collections import defaultdict

N, M = map(int, input().split())
adj_dict = defaultdict(list)

for _ in range(M):
    Sa_i, Sb_i = map(int, input().split())
    adj_dict[Sa_i].append(Sb_i)
    adj_dict[Sb_i].append(Sa_i)

d1, d2 = 0, 0

for node in adj_dict:
    d = len(adj_dict[node])
    
    if d == 1:
        d1 += 1
    elif d == 2:
        d2 += 1
    else:
        print('NO')
        exit()
    
if d1 == 2 and d2 == len(adj_dict) - 2:
    print('YES')
else:
    print('NO')