import java.io.*; import java.util.*; import java.util.stream.*; public class Main { public static void main(String[] args) throws Exception { Scanner sc = new Scanner(); int n = sc.nextInt(); int[] values = new int[n]; for (int i = 0; i < n; i++) { values[i] = sc.nextInt(); } long ans = 0; for (int i = 1; i <= 2000; i++) { int[] add = new int[]{-i - 10, i, -i - 1}; ArrayList> counts = new ArrayList<>(); for (int j = 0; j < 4; j++) { counts.add(new HashMap<>()); } for (int x : values) { for (int j = 2; j >= 0; j--) { if (counts.get(j).containsKey(x + add[j])) { counts.get(j + 1).put(x, counts.get(j + 1).getOrDefault(x, 0L) + counts.get(j).get(x + add[j])); } } counts.get(0).put(x, counts.get(0).getOrDefault(x, 0L) + 1); } for (long x : counts.get(3).values()) { ans += x; } } System.out.println(ans); } } class Utilities { static String arrayToLineString(Object[] arr) { return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n")); } static String arrayToLineString(int[] arr) { return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new)); } } class Scanner { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); StringTokenizer st = new StringTokenizer(""); StringBuilder sb = new StringBuilder(); public Scanner() throws Exception { } public int nextInt() throws Exception { return Integer.parseInt(next()); } public long nextLong() throws Exception { return Long.parseLong(next()); } public double nextDouble() throws Exception { return Double.parseDouble(next()); } public int[] nextIntArray() throws Exception { return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray(); } public String next() throws Exception { while (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }