#include <bits/stdc++.h>
using namespace std;
const int mod = 998244353, INF = 1e9;
int n, m, a[1000002], s[2002], len, l[502], r[502], nex[1000002], num[1000002],
    xyg[1000002];
bool fl[1000002];
long long f[2002][2002];
bool pd(int x, int y) {
  for (int i = x; i <= y; i++)
    if (l[a[s[i]]] < s[x] || r[a[s[i]]] > s[y]) return false;
  return true;
}
long long dp(int x, int y) {
  if (!x || !y) return 0;
  if (y < x) return 1;
  if (l[a[s[y]]] == s[y] && r[a[s[y]]] > l[a[s[y]]] ||
      r[a[s[x]]] == s[x] && r[a[s[x]]] > l[a[s[x]]])
    return 0;
  if (f[x][y] != -1) return f[x][y];
  if (!pd(x, y)) return f[x][y] = 0;
  f[x][y] = 0;
  int Min = INF;
  for (int i = x; i <= y; i++) Min = min(Min, a[s[i]]);
  long long qt = 1;
  for (int i = l[Min]; nex[xyg[i]]; i = nex[i]) {
    i = xyg[i];
    qt = qt * dp(num[i + 1], num[nex[i] - 1]) % mod;
    if (!qt) break;
  }
  if (!qt) return f[x][y] = 0;
  f[x][y] = qt;
  long long s1 = 0, s2 = 0, t;
  for (int i = x; i <= num[l[Min]]; i++) {
    t = 1;
    if (i > x) t = t * dp(x, num[s[i] - 1]) % mod;
    if (i < num[l[Min]]) t = t * dp(num[s[i]], num[l[Min] - 1]) % mod;
    s1 = (s1 + t) % mod;
  }
  for (int i = num[r[Min]]; i <= y; i++) {
    t = 1;
    if (i > num[r[Min]]) t = t * dp(num[r[Min] + 1], num[s[i]]) % mod;
    if (i < y) t = t * dp(num[s[i] + 1], y) % mod;
    s2 = (s2 + t) % mod;
  }
  f[x][y] = f[x][y] * s1 % mod * s2 % mod;
  return f[x][y];
}
int main() {
  memset(f, -1, sizeof(f));
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; i++) scanf("%d", &a[i]);
  xyg[m] = m;
  for (int i = m - 1; i >= 1; i--)
    if (a[i] == a[i + 1])
      xyg[i] = xyg[i + 1];
    else
      xyg[i] = i;
  for (int i = 1; i <= m; i++) {
    nex[r[a[i]]] = i;
    r[a[i]] = i;
  }
  for (int i = m; i >= 1; i--) l[a[i]] = i;
  for (int i = 1; i <= n; i++)
    fl[l[i]] = fl[r[i]] = fl[l[i] - 1] = fl[r[i] + 1] = 1;
  for (int i = 1; i <= m; i++)
    if (fl[i]) {
      s[++len] = i;
      num[i] = len;
    }
  printf("%lld\n", dp(1, len));
  return 0;
}
