MOD = 998244353

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

if N == 0:
    print(1)
else:
    current_L = 1
    current_R = A[0]
    ways = 1
    for i in range(1, N):
        a_i = A[i]
        entry_min = max(current_L, 1)
        entry_max = min(current_R, a_i)
        if entry_max < entry_min:
            print(0)
            exit()
        count = entry_max - entry_min + 1
        ways = (ways * count) % MOD
        current_L = 1
        current_R = a_i
    print(ways)