#include <bits/stdc++.h>
using namespace std;
const int P = 998244353;
const int N = 1000010;
int n, m;
int c[N];
vector<int> colors[510];
int ans = 1;
int dp[510][510];
int l[510], r[510];
int order_l[510], order_r[510];
int tmpl[510], tmpr[510];
int f[N];
vector<pair<int, int>> v[N];
bool cmpl(int x, int y) { return l[x] < l[y]; }
bool cmpr(int x, int y) { return r[x] < r[y]; }
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= m; i++) {
    scanf("%d", &c[i]);
    colors[c[i]].push_back(i);
  }
  set<int> id;
  id.insert(0);
  id.insert(m + 1);
  for (int i = 1; i <= n; i++) {
    assert(!colors[i].empty());
    int l = colors[i].front(), r = colors[i].back();
    auto it = id.lower_bound(l);
    if (*it <= r) {
      printf("0\n");
      return 0;
    }
    it--;
  }
  for (int i = 1; i <= n; i++)
    l[i] = colors[i].front(), r[i] = colors[i].back();
  for (int i = 1; i <= n; i++) order_l[i] = i;
  sort(order_l + 1, order_l + n + 1, cmpl);
  for (int i = 1; i <= n; i++) order_r[i] = i;
  sort(order_r + 1, order_r + n + 1, cmpr);
  l[0] = 0;
  r[0] = m + 1;
  for (int i = n; i; i--) {
    memset(tmpl, 0, sizeof tmpl);
    tmpl[i] = 1;
    for (int j = n; j; j--) {
      for (int k = i; k <= n; k++)
        if (l[c[r[k] + 1]] == r[k] + 1)
          tmpl[order_l[j]] =
              (tmpl[order_l[j]] + 1LL * tmpl[c[r[k] + 1]] * dp[order_l[j]][k]) %
              P;
    }
    memset(tmpr, 0, sizeof tmpr);
    tmpr[i] = 1;
    for (int j = 1; j <= n; j++) {
      for (int k = i; k <= n; k++)
        if (r[c[l[k] - 1]] == l[k] - 1)
          tmpr[order_r[j]] =
              (tmpr[order_r[j]] + 1LL * tmpr[c[l[k] - 1]] * dp[k][order_r[j]]) %
              P;
    }
    for (int j = i; j <= n; j++)
      for (int k = i; k <= n; k++)
        dp[j][k] = (dp[j][k] + 1LL * tmpl[j] * tmpr[k]) % P;
  }
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      v[l[i] - 1].push_back(make_pair(r[j], dp[i][j]));
    }
  f[0] = 1;
  for (int i = 0; i <= m; i++) {
    for (auto p : v[i]) f[p.first] = (f[p.first] + 1LL * p.second * f[i]) % P;
  }
  printf("%d\n", f[m]);
}
