#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
long long dp[2002][4][2002];
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<int>a(n);
	rep(i, n)cin >> a[i];
	rep(i, n) {
		vector<vector<long long>>upd;
		rep2(j, 1, 2002) {
			{
				int fir = a[i] - (j + 10);
				if (fir >= 0) {
					upd.push_back({ fir,1,j,dp[fir][0][j] });
				}
			}
			{
				int fir = a[i] - (10);
				if (fir >= 0) {
					upd.push_back({ fir,2,j,dp[fir][1][j] });
				}
			}
			{
				int fir = a[i] - (j + 10 + 1);
				if (fir >= 0) {
					upd.push_back({ fir,3,j,dp[fir][2][j] });
				}
			}
		}
		rep(j, upd.size()) {
			dp[upd[j][0]][upd[j][1]][upd[j][2]] += upd[j][3];
		}
		rep2(j, 1, 2002)dp[a[i]][0][j]++;
	}
	long long ans = 0;
	rep(i, 2002)rep(j, 2002) ans += dp[i][3][j];
	cout << ans << endl;
	return 0;
}