#include <iostream>
#include <vector>
using namespace std;


#include <atcoder/modint>
using mint = atcoder::modint998244353;

#include <atcoder/lazysegtree>
struct S {
    mint v0, v1;
    int n;
};
S op(S l, S r) {
    return {l.v0 + r.v0, l.v1 + r.v1, l.n + r.n};
}
S e() {
    return {0, 0, 0};
}
struct F {
    mint nsame, ndiff;
};
S mapping(F f, S x) {
    return {x.v0 * f.nsame + x.v1 * f.ndiff, x.v1 * f.nsame + x.v0 * f.ndiff, x.n};
}
F composition(F fnew, F gold) {
    return {fnew.nsame * gold.nsame + fnew.ndiff * gold.ndiff, fnew.nsame * gold.ndiff + fnew.ndiff * gold.nsame};
}
F id() {
    return {1, 0};
}

int main() {
    cin.tie(nullptr), ios::sync_with_stdio(false);
    int N, M;
    cin >> N >> M;

    mint ret = 0;
    vector<S> segtree_init(N + M, e());
    vector<int> seen_last(N);
    for (int i = 0; i < N; ++i) {
        segtree_init[i] = S{1, 0, 1};
        seen_last[N - 1 - i] = i;
    }

    atcoder::lazy_segtree<S, op, e, F, mapping, composition, id> tree(segtree_init);
    int nempty = 0;
    const F f1{mint(N - 1) / N, mint(1) / N};
    for (int t = 0; t < M; ++t) {
        int a;
        cin >> a;
        --a;
        if (a < 0) {
            ++nempty;
            tree.apply(0, N + t, f1);
        } else {
            int l = seen_last[a], r = N + t;
            auto p = tree.prod(l + 1, r);
            ret += tree.get(l).v1 * (N - 1 - p.n) + p.v0;
            tree.set(l, e());
            tree.set(r, S{1, 0, 1});
            seen_last[a] = r;
        }
    }
    cout << (ret + M + mint(N - 1) / 2 * nempty).val() << '\n';
}