#include <bits/stdc++.h>
#define ll long long
#define pii pair <int, int>
#define fi first
#define se second
#define pb push_back

using namespace std;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int N = 2005;
int n, a[N], lim[N], cnt, mk[N]; 

void dfs (int p) {
//	cout << "CHECK:\n"; 
//	for (int i = 0;i < p;i++) cout << a[i] << " "; cout << endl;
//	for (int i = 0;i <= n;i++) cout << mk[i] << " "; cout << endl; 
//	cout << endl; 
	if (p > n) {
		++cnt; 
//		for (int i = 0;i <= n;i++) cout << a[i] << " "; cout << endl;
		return; 
	}
	for (int i = 0;i <= lim[p];i++) {
		if (mk[p] && i != a[p]) continue; 
		a[p] = i;
		int fl = 1; 
		for (int j = 0;j <= p;j++) {
			if (a[j]+a[p-j] > n) {
				fl = 0; break; 
			}
		}
		if (!fl) continue; 
		for (int j = 0;j <= p;j++) {
			if (a[j]+a[p-j] <= p && a[a[j]+a[p-j]] != a[p]) {
				fl = 0; break; 
			}
		}
		if (!fl) continue; 
		for (int j = 0;j <= p;j++) {
			if (a[j]+a[p-j] <= p) continue; 
			if (mk[a[j]+a[p-j]] && a[a[j]+a[p-j]] != a[p]) {
				fl = 0; break; 
			}
		}
		if (!fl) continue; 
		for (int j = 0;j <= p;j++) {
			if (a[j]+a[p-j] > p) {
				mk[a[j]+a[p-j]]++; a[a[j]+a[p-j]] = a[p]; 
			}
		} 
		dfs(p+1);
		for (int j = 0;j <= p;j++) {
			if (a[j]+a[p-j] > p) mk[a[j]+a[p-j]]--; 
		} 
	}
}

void solve () {
	cin >> n; 
	for (int i = 0;i <= n;i++) cin >> lim[i]; 
	dfs(0); 
	cout << cnt; 
}

signed main () {
//	freopen("t.out", "w", stdout); 
	int T = 1;
	while (T--) solve();
	return 0;
}