mod = 998244353

def isgood(n,m,a):
	g = 0
	for i in range(n):
		if i % 2 == 0:
			g += a[i]
		else:
			g -= a[i]
	if g % m == 0:
		return True
	return False

def count(n,m,e,l,t):
	if n % 2 == 0:
		r = (pow(m-1, n, mod) - 1) * pow(m, mod-2, mod) % mod
		if t == 0:
			if e <= 0 < e+l or e <= m < e+l: return (l*r+1) % mod
		else:
			if e-l < 0 <= e or e-l < m <= e: return (l*r+1) % mod
		return l*r % mod
	else:
		r = (pow(m-1, n, mod) + 1) * pow(m, mod-2, mod) % mod
		if t == 1:
			if e-l < 1 <= e or e-l < 1-m <= e: return (l*r-1) % mod
			return l*r % mod
		else:
			if e <= m-1 < e+l or e <= 2*m-1 < e+l: return (l*r-1) % mod
			return l*r % mod

n,m = map(int,input().split())
a = list(map(int,input().split()))

if isgood(n,m,a):
	g = 0
	ans = 0
	for i in range(n):
		ans += count(n-i-1,m,g,a[i],i%2)
		if i%2 == 0:
			g = (g+a[i]) % m
		else:
			g = (g-a[i]) % m
		#print(ans)
	print((ans+1) % mod)
else:
	print(-1)