mod=998244353
N,M=map(int,input().split())
A=list(map(int,input().split()))
S=0
for i in range(N):
  if i&1:
    S-=A[i]
  else:
    S+=A[i]
if S%M:
  print(-1)
  exit()
DP=[[0,0] for i in range(N+1)]
DP[0][1]=1
for i in range(N):
  DP[i+1][1]=(DP[i][0]*(M-1))%mod
  DP[i+1][0]=(DP[i][0]*(M-2)+DP[i][1])%mod
ANS=1
C=[N>>1,(N+1)>>1]
S=0
P=N
for i in range(N):
  P-=1
  if (i^N)&1:
    S=(S-A[i])%M
  else:
    S=(S+A[i])%M
  C[(i^N)&1]-=1
  if C[0]==C[1]:
    if -S%M<A[i]:
      ANS=(ANS+DP[P][1]+DP[P][0]*(A[i]-1))%mod
    else:
      ANS=(ANS+DP[P][0]*A[i])%mod
  else:
    if (S-1)%M<A[i]:
      ANS=(ANS+DP[P][1]+DP[P][0]*(A[i]-1))%mod
    else:
      ANS=(ANS+DP[P][0]*A[i])%mod
print(ANS)