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

#check
q=p[:]
for i in range(n-1):
    q[i+1]+=m-q[i]%m
if q[-1]%m:
    print(-1)
    exit(0)

mod=998244353
ans=0
for i in range(n):
    ans=(ans*(m-1)+p[i])%mod
ans=(ans*pow(m,mod-2,mod)+1)%mod
print(ans)