#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;
  
ll dp[4][2001][2001];

int main() {
  int N;
  cin >> N;
  int A[N];
  for (int i = 0; i < N; ++i) {
    cin >> A[i];
  }

  memset(dp, 0, sizeof(dp));

  for (int i = 0; i < N; ++i) {
    int a = A[i];

    for (int j = 3; j >= 1; --j) {
      for (int k = 1; k <= 2000; ++k) {
        if (j == 1) {
          int a1 = a - (k + 10);
          if (0 <= a1 && a1 <= 2000) {
            dp[j][a][k] += dp[j - 1][a1][k];
          }
        } else if (j == 2) {
          int a2 = a + k;
          if (0 <= a2 && a2 <= 2000) {
            dp[j][a][k] += dp[j - 1][a2][k];
          }
        } else if (j == 3) {
          int a3 = a - (k + 1);
          if (0 <= a3 && a3 <= 2000) {
            dp[j][a][k] += dp[j - 1][a3][k];
          }
        }
      }
    }

    for (int k = 1; k <= 2000; ++k) {
      dp[0][a][k] += 1;
    }
  }

  ll ans = 0;

  for (int a4 = 1; a4 <= 2000; ++a4) {
    for (int k = 1; k <= 2000; ++k) {
      ans += dp[3][a4][k];
    }
  }

  cout << ans << endl;

  return 0;
}