#include <bits/stdc++.h>
using namespace std;
void Freopen() {
  freopen(
      "title"
      ".in",
      "r", stdin);
  freopen(
      "title"
      ".out",
      "w", stdout);
}
int read() {
  int g = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || '9' < ch) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while ('0' <= ch && ch <= '9') {
    g = g * 10 + ch - '0';
    ch = getchar();
  }
  return g * f;
}
const int N = 505;
const int INF = 1e9;
const int M = 1e6 + 5;
const int mod = 998244353;
int s[N << 1][N << 1], n, m, a[M], cnt;
vector<int> pos[N];
int dfs(int l, int r) {
  if (l > r) return 1;
  if (~s[l][r]) return s[l][r];
  int mi = INF;
  for (int i = (l); i <= (r); i++) mi = min(mi, a[i]);
  int L = pos[mi][0], R = pos[mi][pos[mi].size() - 1], al = 0, ar = 0, ans;
  if (L < l || R > r) return s[l][r] = 0;
  for (int i = (l); i <= (L); i++)
    al = (al + 1ll * dfs(l, i - 1) * dfs(i, L - 1) % mod) % mod;
  for (int i = (R); i <= (r); i++)
    ar = (ar + 1ll * dfs(R + 1, i) * dfs(i + 1, r) % mod) % mod;
  ans = 1ll * al * ar % mod;
  for (int i = (0); i <= ((int)pos[mi].size() - 2); i++)
    ans = 1ll * ans * dfs(pos[mi][i] + 1, pos[mi][i + 1] - 1) % mod;
  return s[l][r] = ans;
}
signed main() {
  n = read(), m = read();
  for (int i = (1); i <= (m); i++) a[i] = read();
  int cnt = 0;
  for (int i = (1); i <= (m); i++) {
    if (a[i] == a[i + 1]) continue;
    a[++cnt] = a[i];
  }
  if (cnt > 2 * n) return cout << 0, signed();
  for (int i = (1); i <= (cnt); i++) pos[a[i]].push_back(i);
  memset(s, -1, sizeof(s));
  return cout << dfs(1, cnt), signed();
}
