#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
const i64 P = 998244353;
i64 dp[1234][1234];
int a[1234567], n, m, t, posl[1234], posr[1234];
i64 solve(int l, int r) {
  if (dp[l][r] != -1) return dp[l][r];
  if (l > r) return 1;
  i64 &val = dp[l][r];
  val = 0;
  int minc = a[l];
  for (int j = l; j <= r; j++) {
    minc = min(minc, a[j]);
  }
  int prepos = -1;
  i64 tmpval = 1;
  for (int j = l; j <= r; j++) {
    if (a[j] == minc) {
      if (prepos != -1) {
        tmpval = tmpval * solve(prepos + 1, j - 1) % P;
      }
      prepos = j;
    }
  }
  i64 lval = 0;
  for (int j = l; j <= posl[minc]; j++) {
    lval = (lval + solve(l, j - 1) * solve(j, posl[minc] - 1)) % P;
  }
  i64 rval = 0;
  for (int j = posr[minc]; j <= r; j++) {
    rval = (rval + solve(posr[minc] + 1, j) * solve(j + 1, r)) % P;
  }
  return val = tmpval * lval % P * rval % P;
}
int main() {
  memset(dp, -1, sizeof(dp));
  scanf("%d%d", &n, &m);
  int c = 0;
  for (int i = 1; i <= m; i++) {
    int x;
    scanf("%d", &x);
    if (x != c) a[++t] = x;
    c = x;
  }
  if (t >= 2 * n) {
    printf("%d\n", 0);
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    int l = t + 1, r = 0;
    for (int j = 1; j <= t; j++) {
      if (a[j] == i) {
        l = min(l, j);
        r = max(r, j);
      }
    }
    for (int j = l; j <= r; j++)
      if (a[j] < i) {
        printf("%d\n", 0);
        return 0;
      }
    posl[i] = l;
    posr[i] = r;
  }
  printf("%lld\n", solve(1, t));
}
