#include <bits/stdc++.h>   using namespace std;   const long long mod = 998244353;   const long long N = 5e2 + 1;   const long long M = 1e6 + 1;   long long dp[2 * N][2 * N], min1[2 * N][2 * N], ar[2 * N], ar1[M];   bool check[2 * N][2 * N];   vector<long long> occur[N];   long long solve(long long l, long long r) {     if (l > r) {       return 1;     }     if (check[l][r]) {       return dp[l][r];     }     long long y = min1[l][r];     if (occur[y][0] < l || occur[y][occur[y].size() - 1] > r) {       check[l][r] = true;       return 0;     }     if (l == r) {       check[l][r] = true;       dp[l][r] = 1;       return dp[l][r];     }     check[l][r] = true;     long long tich = 1, sum = solve(l, occur[y][0] - 1),               sum1 = solve(occur[y][occur[y].size() - 1] + 1, r), i;     if (l <= occur[y][0] - 1) {       sum *= 2;     }     if (occur[y][occur[y].size() - 1] + 1 <= r) {       sum1 *= 2;     }     for (i = 0; i + 1 < occur[y].size(); i++) {       tich *= solve(occur[y][i] + 1, occur[y][i + 1] - 1);       tich %= mod;     }     for (i = l; i < occur[y][0] - 1; i++) {       sum += solve(l, i) * solve(i + 1, occur[y][0] - 1);       sum %= mod;     }     for (i = occur[y][occur[y].size() - 1] + 1; i < r; i++) {       sum1 += solve(occur[y][occur[y].size() - 1] + 1, i) * solve(i + 1, r);       sum1 %= mod;     }     dp[l][r] = ((sum * sum1) % mod * tich) % mod;     return dp[l][r];   }   signed main() {     ios::sync_with_stdio(0);     cin.tie(0);     long long n, m, i, j, k, l = 0;     cin >> n >> m;     ar1[0] = -1;     for (i = 1; i <= m; i++) {       cin >> ar1[i];       if (ar1[i] != ar1[i - 1]) {         l++;         ar[l] = ar1[i];         if (l > 2 * n + 1) {           cout << 0;           exit(0);         }       }     }     n = l;     for (i = 1; i <= n; i++) {       min1[i][i] = ar[i];       occur[ar[i]].push_back(i);       for (j = i + 1; j <= n; j++) {         min1[i][j] = min(min1[i][j - 1], ar[j]);       }     }     cout << solve(1, n);   }   