#include <bits/stdc++.h>
using namespace std;
const long long MOD = 998244353;
struct intmod {
  long long val;
  intmod(long long _val = 1) {
    val = _val % MOD;
    if (val < 0) val += MOD;
  }
  bool operator!=(intmod rhs) const { return val != rhs.val; }
  bool operator==(intmod rhs) const { return val == rhs.val; }
  intmod operator+=(intmod rhs) {
    val += rhs.val;
    if (val >= MOD) val -= MOD;
    return *this;
  }
  intmod operator-=(intmod rhs) {
    val -= rhs.val;
    if (val < 0) val += MOD;
    return *this;
  }
  intmod operator*=(intmod rhs) {
    val = val * rhs.val % MOD;
    return *this;
  }
  friend intmod operator+(intmod lhs, intmod rhs) { return lhs += rhs; }
  friend intmod operator-(intmod lhs, intmod rhs) { return lhs -= rhs; }
  friend intmod operator*(intmod lhs, intmod rhs) { return lhs *= rhs; }
  friend intmod sqr(intmod a) { return a * a; }
  friend intmod bpow(intmod a, int p) {
    intmod ans(1);
    while (p) {
      if (p & 1) ans *= a;
      a = sqr(a);
      p >>= 1;
    }
    return ans;
  }
  friend intmod inv(intmod a) { return bpow(a, MOD - 2); }
  intmod operator/=(intmod rhs) { return (*this) *= inv(rhs); }
  friend intmod operator/(intmod lhs, intmod rhs) { return lhs /= rhs; }
  friend istream &operator>>(istream &is, intmod &im) { return is >> im.val; }
  friend ostream &operator<<(ostream &os, intmod im) { return os << im.val; }
};
const int MAXN = 517, MAXM = 1000030, LOG = 21;
intmod F0[MAXN][MAXN], F1[MAXN][MAXN];
intmod solve(vector<int> vec) {
  int N = ((int)vec.size());
  vec.insert(vec.begin(), MAXN);
  for (int i = 0; i <= N + 1; ++i)
    for (int j = 0; j <= N + 1; ++j) F0[i][j] = F1[i][j] = 1;
  for (int i = 1; i <= N; ++i) F0[i][i] = F1[i][i] = 1;
  for (int len = 2; len <= N; ++len)
    for (int l = 1; l <= N - len + 1; ++l) {
      int r = l + len - 1, m = l;
      for (int i = l + 1; i <= r; ++i)
        if (vec[i] < vec[m]) m = i;
      F0[l][r] = F1[l][m - 1] * F1[m + 1][r];
      F1[l][r] = 0;
      for (int i = l; i <= r; ++i) F1[l][r] += F0[l][i] * F1[i + 1][r];
    }
  return F1[1][N];
}
int N, M;
int A[MAXM], L[MAXN], R[MAXN];
int st[MAXN], rr = 0;
vector<int> vec[MAXN * 2];
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  scanf("%d %d", &N, &M);
  for (int i = 1; i <= M; ++i) scanf("%d", &A[i]);
  for (int i = 1; i <= M; ++i) {
    R[A[i]] = i;
    if (!L[A[i]]) L[A[i]] = i;
  }
  int ptr = N + 1;
  for (int i = 1; i <= M; ++i) {
    int last = (rr > 0 ? st[rr - 1] : 0);
    if (last > A[i]) {
      puts("0");
      return 0;
    }
    if (L[A[i]] == i) {
      vec[last].push_back(A[i]);
      st[rr++] = A[i];
    }
    if (A[i] == last && !vec[last].empty()) vec[ptr++].swap(vec[last]);
    if (R[A[i]] == i) --rr;
  }
  assert(ptr < MAXN * 2);
  intmod ans = 1;
  for (int i = 0; i <= ptr; ++i)
    if (!vec[i].empty()) ans *= solve(vec[i]);
  cout << ans << endl;
  return 0;
}
