N,M=map(int,input().split())
*nums,=map(int,input().split())
in_nums=[0]*(N+1)
for n in nums:
    in_nums[n]=1
max_idx=1
ans=1
MOD=119<<23|1
for i in range(M-1):
    if nums[i]>nums[i+1]:
        break
    max_idx+=1
if sum(in_nums[:nums[0]])!=nums[0]-1:
    print(0)
    exit(0)
curr_idx=0
adder=0
for curr_num in range(nums[0]+1,N+1):
    if in_nums[curr_num]:
        continue
    while curr_idx<max_idx and curr_num>nums[curr_idx]:
        curr_idx+=1
    ans=ans*(curr_idx+1+adder)%MOD
    adder+=1
print(ans)