#include <cstdio>
#include <cctype>

template <typename T> T read() {
  T res = 0, f = 1;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar()) if (ch == '-') f = -1;
  for (; isdigit(ch); ch = getchar()) res = (res << 3) + (res << 1) + (ch ^ 48);
  return res * f;
}

void write(__int128 x, char ed = '\n') {
  if (x < 0) x = -x, putchar('-');
  static int sta[64], top = 0;
  do {
    sta[++top] = x % 10;
    x /= 10;
  } while (x);
  while (top) {
    putchar(sta[top--] ^ 48);
  }
  putchar(ed);
}

template <typename T> void write(T x, char ed = '\n') {
  write((__int128)x, ed);
}

#include <cstring>
const int MOD = 998244353;

int n;
int a[2010];
int team[2010];
int teamcnt[2010];
int ans;

bool check() {
  for (int i = 1; i <= n; ++i) {
    teamcnt[i] = 0;
  }
  for (int i = 1; i <= n; ++i) {
    teamcnt[team[i]]++;
    if (a[i] < teamcnt[team[i]]) return false;
  }
  return true;
}

void dfs(int now) {
  if (now > n) {
    if (check()) if (++ans == MOD) ans = 0;
    return ;
  }
  for (int i = team[now - 1]; i <= team[now - 1] + 1; ++i) {
    team[now] = i;
    dfs(now + 1);
  }
}

int main() {
  #ifdef LOCAL
    freopen("!input.in", "r", stdin);
    freopen("!output.out", "w", stdout);
  #else
    freopen("gamem.in", "r", stdin);
    freopen("gamem.out", "w", stdout);
  #endif
  n = read<int>();
  for (int i = 1; i <= n; ++i) {
    a[i] = read<int>();
  }

  team[1] = 1;
  dfs(2);

  write(ans);
  return 0;
}