def cmb(n, r, mod):#コンビネーションの高速計算　
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return (g1[n] * g2[r] %mod) * g2[n-r] % mod

mod = 998244353#出力の制限
N = 5*10**3
g1 = [1]*(N+1) # 元テーブル
g2 = [1]*(N+1) #逆元テーブル
inverse = [1]*(N+1) #逆元テーブル計算用テーブル

for i in range( 2, N + 1 ):
    g1[i]=( ( g1[i-1] * i ) % mod )
    inverse[i]=( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2[i]=( (g2[i-1] * inverse[i]) % mod )
inverse[0]=0

def solve(N,M,A):
    N,M = M,N
    A = [0] + A

    B = [0 for i in range(M+1)]
    for i in range(N+1):
        for j in range(A[i]+1,M+1):
            B[j] = i

    dp = [[0 for j in range(M+2)] for i in range(M+1)]

    for i in range(1,M+1):
        n = B[i]
        for j in range(A[n],-1,-1):
            rest = i-j
            if i!=A[n]+1:
                dp[i][j] = A[n+1] + (i-A[n]) * dp[i-1][j] + (A[n]-j) * dp[i][j+1]
                dp[i][j] %= mod
                dp[i][j] *= inverse[rest]
                dp[i][j] %= mod
            else:
                if n==0:
                    dp[i][j] = A[n+1]
                else:
                    dp[i][j] = A[n+1] + (A[n]-j) * dp[i][j+1]
                    dp[i][j] %= mod
                    for k in range(min(j+1,A[n]-A[n-1]+1)):
                        tmp = dp[i-1-k][j-k] * cmb(A[n]-A[n-1],k,mod) % mod
                        tmp = tmp * cmb(A[n-1],j-k,mod) % mod
                        tmp = tmp * ((g2[A[n]] * g1[A[n]-j] % mod) * g1[j] % mod) % mod
                        dp[i][j] += tmp
                        dp[i][j] %= mod
                    dp[i][j] *= inverse[rest]
                    dp[i][j] %= mod

    return dp[M][0]

N,M = map(int,input().split())
A = list(map(int,input().split()))
print(solve(N,M,A))