#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
ll mod=998244353;
ll inva(ll N) {
    ll a = N, b = mod, c = 1, d = 0;
    while (b > 0) {
        ll t = a / b;
        a -= t * b;
        swap(a, b);
        c -= t * d;
        swap(c, d);

    }
    c %= mod;
    if (c < 0)c += mod;
    return c;

}//割り算時に使う逆元を求める.


int main() {
    ll N,M;
    cin>>N>>M;
    set<ll> A;
    rep(i,M){
        ll Ai;
        cin>>Ai;
        A.insert(Ai);
    }
    vll B(N);
    ll an=0;
    rep(i,N){
        B[i]=*A.lower_bound(i+1);
        an+=B[i]*inva(N-i);
        an%=mod;

    }
    cout<<an<<endl;
    
}