import java.util.*; class Main3 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); int[] arr = new int[n]; for (int i = 0; i < n; i++) { arr[i] = sc.nextInt(); } HashMap<Integer, Integer> hm = new HashMap<>(); for (int i = 1; i < n; i++) { int t = hm.getOrDefault(arr[i], 0); t++; hm.put(arr[i], t); } long ans = 0; for (int j = 1; j + 1 < n; j++) { hm.put(arr[j], hm.getOrDefault(arr[j], 1) - 1); for (int i = 0; i < j; i++) { int t = 3 * arr[j] - arr[i]; ans += hm.getOrDefault(t, 0); } } System.out.println(ans); } }