import sys
input = sys.stdin.readline

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

mod=998244353

DP=[0,0,0,0]
DP[1]=min(A[0],A[1])
DP[2]=max(A[0],A[1])-min(A[0],A[1])
DP[3]=M-DP[1]-DP[2]

A.append(1)

for i in range(N-1):
    NDP=[0,0,0,0]
    NDP[0]+=DP[0]*M

    if A[i]<A[i+1]:
        if A[i+1]<A[i+2]:
            NDP[0]+=DP[1]*(A[i+1]-A[i])

            NDP[1]+=DP[1]*A[i]
            NDP[2]+=DP[1]*(A[i+2]-A[i+1])
            NDP[3]+=DP[1]*(M-A[i+2])


            NDP[1]+=DP[2]*A[i+1]
            NDP[2]+=DP[2]*(A[i+2]-A[i+1])
            NDP[3]+=DP[2]*(M-A[i+2])


            NDP[0]+=DP[3]*(A[i+1]-A[i])

            NDP[1]+=DP[3]*A[i]
            NDP[2]+=DP[3]*(A[i+2]-A[i+1])
            NDP[3]+=DP[3]*(M-A[i+2])

        elif A[i]<A[i+2]<=A[i+1]:
            NDP[0]+=DP[1]*(A[i+1]-A[i])

            NDP[1]+=DP[1]*A[i]
            NDP[3]+=DP[1]*(M-A[i+1])

            NDP[1]+=DP[2]*A[i+2]
            NDP[2]+=DP[2]*(A[i+1]-A[i+2])
            NDP[3]+=DP[2]*(M-A[i+1])


            NDP[0]+=DP[3]*(A[i+1]-A[i])

            NDP[1]+=DP[3]*A[i]
            NDP[3]+=DP[3]*(M-A[i+1])

        elif A[i+2]<=A[i]:
            NDP[0]+=DP[1]*(A[i+1]-A[i])

            NDP[1]+=DP[1]*A[i+2]
            NDP[2]+=DP[1]*(A[i]-A[i+2])
            NDP[3]+=DP[1]*(M-A[i+1])


            NDP[1]+=DP[2]*A[i+2]
            NDP[2]+=DP[2]*(A[i+1]-A[i+2])
            NDP[3]+=DP[2]*(M-A[i+1])


            NDP[0]+=DP[3]*(A[i+1]-A[i])

            NDP[1]+=DP[3]*A[i+2]
            NDP[2]+=DP[3]*(A[i]-A[i+2])
            NDP[3]+=DP[3]*(M-A[i+1])

    else:
        if A[i]<A[i+2]:
            NDP[1]+=DP[1]*A[i+1]
            NDP[2]+=DP[1]*(A[i+2]-A[i+1])
            NDP[3]+=DP[1]*(M-A[i+2])


            NDP[0]+=DP[2]*(A[i+1]+(M-A[i]))

            NDP[2]+=DP[2]*(A[i]-A[i+1])

            NDP[1]+=DP[3]*A[i+1]
            NDP[2]+=DP[3]*(A[i+2]-A[i+1])
            NDP[3]+=DP[3]*(M-A[i+2])

        elif A[i+1]<A[i+2]<=A[i]:
            NDP[1]+=DP[1]*A[i+1]
            NDP[2]+=DP[1]*(A[i+2]-A[i+1])
            NDP[3]+=DP[1]*(M-A[i+2])


            NDP[0]+=DP[2]*(A[i+1]+(M-A[i]))

            NDP[2]+=DP[2]*(A[i+2]-A[i+1])
            NDP[3]+=DP[2]*(A[i]-A[i+2])

            NDP[1]+=DP[3]*A[i+1]
            NDP[2]+=DP[3]*(A[i+2]-A[i+1])
            NDP[3]+=DP[3]*(M-A[i+2])

        elif A[i+2]<=A[i+1]:
            NDP[1]+=DP[1]*A[i+2]
            NDP[2]+=DP[1]*(A[i+1]-A[i+2])
            NDP[3]+=DP[1]*(M-A[i+1])


            NDP[0]+=DP[2]*(A[i+1]+(M-A[i]))

            NDP[3]+=DP[2]*(A[i]-A[i+1])

            NDP[1]+=DP[3]*A[i+2]
            NDP[2]+=DP[3]*(A[i+1]-A[i+2])
            NDP[3]+=DP[3]*(M-A[i+1])


    DP=NDP
    DP[0]%=mod
    DP[1]%=mod
    DP[2]%=mod

    #print(DP)


ANS=0
k=pow(M,N-1,mod)

for i in range(N):
    ANS+=k*(M-A[i])%mod

print((ANS+DP[0])%mod)