N, M = map(int, raw_input().split())
rinsetsu = [[] for _ in xrange(N)]
for _ in xrange(M):
    a, b = map(int, raw_input().split())
    rinsetsu[a-1].append(b-1)
    rinsetsu[b-1].append(a-1)

v2v3 = [(u, v) for u in rinsetsu[0] for v in rinsetsu[u] if v != 0]

for i in xrange(len(v2v3)):
    for j in xrange(i+1, len(v2v3)):
        v2, v3 = v2v3[i]
        v5, v4 = v2v3[j]
        if v2 != v5 and v3 != v4 and v3 in rinsetsu[v4]:
            print 'YES'
            exit()
print 'NO'