from heapq import heappop, heappush

N, K = map(int, input().split())
A = list(map(int, input().split()))
h = []
over = set(A)
for i in range(K):
    heappush(h,-A[i])

cnt,bf = 0, 1<<60
while h:
    v = -heappop(h)
    if v+1==bf:cnt+=1
    else:cnt=1
    bf = v

    if cnt>=4:exit(print('No'))
    # 1,6
    if v+5 in over and v-1 not in over and v-1>0:
        over.add(v-1)
        heappush(h,-(v-1))
    # 2,5
    if v+3 in over and v-2 not in over and v-2>0:
        over.add(v-2)
        heappush(h,-(v-2))
    # 3,4
    if v+1 in over and v-3 not in over and v-3>0:
        over.add(v-3)
        heappush(h,-(v-3))

print('No' if 1 in over else 'Yes')