#include <bits/stdc++.h>
using namespace std;
const int MAXM = 1e6 + 1, MAXN = 501, MOD = 998244353;
int n, m, c[MAXM], s[MAXN], d[MAXN], memo[MAXN][MAXN], last[MAXN], nxt[MAXM];
int dp(int l, int r) {
  if (!l) return 1;
  if (l != r) {
    if (d[l] >= d[r]) return 1;
    if (s[l] >= s[r]) return 1;
  }
  if (memo[l][r] != -1) {
    return memo[l][r];
  }
  int i = l;
  bool same = 1;
  for (int j = 1; j <= n; j++) {
    if (s[j] >= s[l] && s[j] <= d[r] && d[j] >= s[l] && d[j] <= d[r]) {
      if (j != l) same = 0;
      i = min(i, j);
    }
  }
  if (same) return memo[l][r] = 1;
  long long f = 0, k = 0;
  if (i == l)
    f = 1;
  else {
    int lo = c[s[i]];
    while (s[lo] >= s[l]) {
      if (!lo) break;
      long long tmp = 1;
      (tmp *= dp(lo, c[s[i] - 1])) %= MOD;
      (tmp *= dp(l, c[s[lo] - 1])) %= MOD;
      (f += tmp) %= MOD;
      lo = (s[lo] > 0 ? c[s[lo] - 1] : 0);
    }
  }
  if (i == r)
    k = 1;
  else {
    int hi = c[d[i]];
    while (s[hi] <= d[r]) {
      if (!hi) break;
      long long tmp = 1;
      (tmp *= dp(c[d[i] + 1], hi)) %= MOD;
      (tmp *= dp(c[d[hi] + 1], r)) %= MOD;
      (k += tmp) %= MOD;
      hi = (d[hi] < d[r] ? c[d[hi] + 1] : 0);
    }
  }
  long long res = (f * k) % MOD;
  int start = s[i];
  while (nxt[start] != -1) {
    if (nxt[start] - start > 1)
      (res *= dp(c[start + 1], c[nxt[start] - 1])) %= MOD;
    start = nxt[start];
  }
  return memo[l][r] = res;
}
bool wrong() {
  for (int i = 1; i <= n; i++) {
    for (int j = s[i]; j <= d[i]; j++) {
      if (c[j] < i) return 1;
    }
  }
  return 0;
}
void magic() {
  memset(d, 0, sizeof(d));
  for (int i = 1; i <= n; i++) s[i] = m;
  for (int i = 0; i < m; i++) {
    s[c[i]] = min(s[c[i]], i);
    d[c[i]] = max(d[c[i]], i);
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  memset(last, -1, sizeof(last));
  memset(nxt, -1, sizeof(nxt));
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    cin >> c[i];
    if (last[c[i]] != -1) nxt[last[c[i]]] = i;
    last[c[i]] = i;
  }
  magic();
  if (wrong()) {
    cout << "0";
    exit(0);
  }
  memset(memo, -1, sizeof(memo));
  cout << dp(c[0], c[m - 1]);
  return 0;
}
