#include <bits/stdc++.h>
using namespace std;
const long long MOD = 998244353;
const int base = 1048576;
int T[4 * 1010101];
int L[505];
int R[505];
long long D[505][505];
int C[1010101];
int N, M;
int bef[505];
vector<int> loc[505];
void maketree() {
  for (int i = 1; i <= M; i++) T[base + i - 1] = C[i];
  for (int i = base - 1; i >= 1; i--) T[i] = min(T[i * 2], T[i * 2 + 1]);
}
int query(int s, int e) {
  int l = base + s, r = base + e;
  l--;
  r--;
  int ret = N + 1;
  while (l <= r) {
    if (l & 1) {
      ret = min(ret, T[l]);
      l++;
    }
    if (!(r & 1)) {
      ret = min(ret, T[r]);
      r--;
    }
    l >>= 1;
    r >>= 1;
  }
  return ret;
}
long long f(int l, int r) {
  if (R[r] == L[l]) return 1;
  if (L[l] > R[r]) return 1;
  if (D[l][r] != -1) return D[l][r];
  int m = query(L[l], R[r]);
  long long t = 1;
  for (int i = 1; i < loc[m].size(); i++) {
    if (loc[m][i] - loc[m][i - 1] == 1) continue;
    t = t * f(C[loc[m][i - 1] + 1], C[loc[m][i] - 1]) % MOD;
  }
  long long sl = 0, sr = 0;
  int lidx = loc[m][0] - 1;
  if (lidx < L[l])
    sl = 1;
  else {
    while (1) {
      if (lidx >= L[l])
        sl = (sl + f(C[lidx + 1], C[loc[m][0] - 1]) * f(l, C[lidx])) % MOD;
      else
        sl = (sl + f(C[lidx + 1], C[loc[m][0] - 1])) % MOD;
      if (lidx < L[l]) break;
      lidx = L[C[lidx]] - 1;
    }
  }
  int ridx = loc[m].back() + 1;
  if (ridx > R[r])
    sr = 1;
  else {
    while (1) {
      if (ridx <= R[r])
        sr = (sr + f(C[loc[m].back() + 1], C[ridx - 1]) * f(C[ridx], r)) % MOD;
      else
        sr = (sr + f(C[loc[m].back() + 1], C[ridx - 1])) % MOD;
      if (ridx > R[r]) break;
      ridx = R[C[ridx]] + 1;
    }
  }
  return D[l][r] = t * sl % MOD * sr % MOD;
}
int main() {
  scanf("%d%d", &N, &M);
  for (int i = 1; i <= N; i++) {
    L[i] = M + 1;
    R[i] = 0;
  }
  C[M + 1] = N + 1;
  L[N + 1] = R[N + 1] = N + 1;
  for (int i = 1; i <= M; i++) {
    scanf("%d", &C[i]);
    L[C[i]] = min(L[C[i]], i);
    R[C[i]] = max(R[C[i]], i);
    loc[C[i]].push_back(i);
  }
  maketree();
  for (int i = 1; i <= M; i++) {
    if (bef[C[i]] && query(bef[C[i]] + 1, i - 1) < C[i]) {
      puts("0");
      return 0;
    }
    bef[C[i]] = i;
  }
  for (int i = 1; i <= N; i++) {
    for (int j = 1; j <= N; j++) {
      D[i][j] = -1;
    }
  }
  printf("%lld\n", f(C[1], C[M]));
  return 0;
}
