MOD = 998244353

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

sum0 = 0
sum1 = 0
for i, a in enumerate(A):
    if i%2 == 0:
        sum0 += a
        sum0 %= M
    else:
        sum1 += a
        sum1 %= M
if sum0 != sum1:
    exit(print(-1))

C = [0, 1]
for n in range(2, N+1):
    C.append(C[-1]*(M-1)%MOD)
    if n%2 == 0:
        C[-1] -= 1
        C[-1] %= MOD
    else:
        C[-1] += 1
        C[-1] %= MOD

SUM = 0
ans = 1
a, b = (N+1)//2, N//2
for i in range(N):
    if i%2 == 0:
        a -= 1
    else:
        b -= 1
    if A[i] == 0: continue

    c, d = C[a], C[b]
    ans += A[i]*c%MOD*d%MOD*M%MOD
    ans %= MOD

    if a%2 == 0:
        ans += A[i]*d%MOD
        ans %= MOD
    else:
        ans -= A[i]*d%MOD
        ans %= MOD
    if b%2 == 0:
        ans += A[i]*c%MOD
        ans %= MOD
    else:
        ans -= A[i]*c%MOD
        ans %= MOD

    if i%2 == 0:
        l, r = SUM, SUM+A[i]-1
    else:
        l, r = SUM-A[i]+1, SUM
    l %= M
    r %= M
    if l > r: r += M
    m = (b-a)%M
    if l <= m <= r or l <= m+M <= r:
        if (a+b)%2 == 0:
            ans += 1
            ans %= MOD
        else:
            ans -= 1
            ans %= MOD

    if i%2 == 0:
        SUM += A[i]
        SUM %= M
    else:
        SUM -= A[i]
        SUM %= M

print(ans)