# O(N*M)

n,m=map(int,input().split())
a=list(map(int,input().split()))
odd=0
even=0
for i in range(n):
  if i%2==0:
    odd+=a[i]
  else:
    even+=a[i]
if (odd-even)%m!=0:
  print(-1)
  exit()
if n*m>=5*10**7:
  raise Exception

mod=998244353
M=m-1
powM=[1]

for i in range(n+10):
  powM.append(powM[-1]*M%mod)
invm=pow(m,mod-2,mod)
ans=0
res=0
for i in range(n):
  ai=a[i]
  k=n-1-i
  x=powM[k]
  if k%2==0:
    y=(x-1)*invm
    y%=mod
  else:
    y=(x+1)*invm
    y%=mod
  for j in range(ai):
    if k%2==0:
      if (res+j)%m==0:
        ans+=y+1
      else:
        ans+=y
    else:
      if (res-j+m-1)%m==0:
        ans+=y-1
      else:
        ans+=y
  if i%2==0:
    res+=ai
  else:
    res-=ai
  ans%=mod
  #print(x,y)
ans+=1
print(ans%mod)