#include <bits/stdc++.h>
const int MOD = 998244353;
int cs[1000005];
int ds[1000005];
int ds_len = 0;
int first[1000][1000];
int dp[1000][1000];
std::vector<int> where[501];
int left[501];
int right[501];
int core[501];
int get_dp(int l, int r);
int get_core(int c) {
  if (core[c] != -1) return core[c];
  int res = 1;
  for (int i = 0; i + 1 < where[c].size(); i++) {
    int a = where[c][i], b = where[c][i + 1];
    res = 1LL * res * get_dp(a + 1, b - 1) % MOD;
  }
  core[c] = res;
  return core[c];
}
int get_dp(int l, int r) {
  if (l > r) return 1;
  if (dp[l][r] != -1) return dp[l][r];
  int c = first[l][r];
  int lsum = 0, rsum = 0;
  for (int a = l; a <= left[c]; a++) {
    lsum = (lsum + 1LL * get_dp(l, a - 1) * get_dp(a, left[c] - 1)) % MOD;
  }
  for (int b = right[c]; b <= r; b++) {
    rsum = (rsum + 1LL * get_dp(right[c] + 1, b) * get_dp(b + 1, r)) % MOD;
  }
  dp[l][r] = 1LL * lsum * get_core(c) % MOD * rsum % MOD;
  return dp[l][r];
}
int main() {
  int N, M;
  scanf("%d %d", &N, &M);
  for (int i = 0; i < M; i++) {
    scanf("%d", &cs[i]);
  }
  for (int i = 0; i < M; i++) {
    if (i == 0 || cs[i] != cs[i - 1]) {
      ds[ds_len++] = cs[i];
    }
  }
  if (ds_len > N * 2) {
    printf("0\n");
    return 0;
  }
  for (int i = 0; i < ds_len; i++) {
    first[i][i] = ds[i];
  }
  for (int l = 0; l < ds_len; l++) {
    for (int r = l + 1; r < ds_len; r++) {
      first[l][r] = std::min(first[l][r - 1], ds[r]);
    }
  }
  for (int i = 0; i < ds_len; i++) {
    where[ds[i]].push_back(i);
  }
  for (int c = 1; c <= N; c++) {
    assert(where[c].size());
    left[c] = where[c].front();
    right[c] = where[c].back();
  }
  for (int i = ds_len - 1; i >= 0; i--) {
    left[ds[i]] = i;
  }
  for (int i = 1; i <= N; i++) {
    if (first[left[i]][right[i]] < i) {
      printf("0\n");
      return 0;
    }
  }
  for (int i = 0; i < ds_len; i++) {
    for (int j = 0; j < ds_len; j++) {
      dp[i][j] = -1;
    }
  }
  for (int i = 1; i <= N; i++) {
    core[i] = -1;
  }
  printf("%d\n", get_dp(0, ds_len - 1));
}
