class BIT():
    def __init__(self,n,mod=None):
        self.BIT=[0]*(n+1)
        self.num=n
        self.mod = mod

    def query(self,idx):
        res_sum = 0
        while idx > 0:
            res_sum += self.BIT[idx]
            if self.mod:
                res_sum %= self.mod
            idx -= idx&(-idx)
        return res_sum

    #Ai += x O(logN)
    def update(self,idx,x):
        while idx <= self.num:
            self.BIT[idx] += x
            if self.mod:
                self.BIT[idx] %= self.mod
            idx += idx&(-idx)
        return

import sys,random,bisect
from collections import deque,defaultdict
from heapq import heapify,heappop,heappush
from itertools import permutations
from math import log,gcd

input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

mod = 998244353
i2 = pow(2,mod-2,mod)

def solve(N,M,A):
    p = ((N-2)*pow(N,mod-2,mod)) % mod
    ip = pow(p,mod-2,mod)

    A = [N-i for i in range(N)] + A
    A = [-1] + A

    zero = [A[i]==0 for i in range(N+M+1)]
    for i in range(1,N+M+1):
        zero[i] += zero[i-1]
    Z = zero[-1]

    lastappear = [N-i+1 for i in range(N+1)]
    res = 0
    bit_p = BIT(N+M,mod=998244353)
    bit_cnt = BIT(N+M)
    for i in range(1,N+1):
        bit_cnt.update(i,1)
        bit_p.update(i,pow(ip,zero[i],mod))

    for i in range(N+1,N+M+1):
        if A[i]==0:
            res += (N-1)
            res %= mod
        else:
            pre = lastappear[A[i]]
            k = bit_cnt.query(pre-1)

            res += (N-1-k) % mod
            res %= mod
            res += (bit_p.query(i)-bit_p.query(pre)) * pow(p,zero[i],mod) % mod
            res %= mod

            res += k % mod
            res %= mod
            res -= k * pow(p,zero[i]-zero[pre],mod) % mod
            res %= mod

            bit_cnt.update(pre,-1)
            bit_p.update(pre,-pow(ip,zero[pre],mod))

            lastappear[A[i]] = i
            bit_cnt.update(i,1)
            bit_p.update(i,pow(ip,zero[i],mod))

    res *= i2
    res %= mod
    res +=  M
    res %= mod

    return res

N,M = mi()
A = li()

print(solve(N,M,A))