#!/bin/python3

import math
import os
import random
import re
import sys

def solve(V):
    n = len(V)
    meets = (n // 2) * (n - n // 2) * 2 * 2 * 10**5

    V.sort()

    pos = 0
    while pos < n and (V[pos] - V[pos - 1]) % 1000 <= 1:
        pos += 1

    run = 0
    for i in range(pos, pos + n):
        if (V[i % n] - V[(i - 1) % n]) % 1000 == 1:
            run += 1
        else:
            if run > 0:
                meets += (run + 1) // 2 * 2
                run = 0

    if run > 0:
        meets += (run + 1) // 2 * 2

    return meets


if __name__ == '__main__':
    fptr = open(os.environ['OUTPUT_PATH'], 'w')

    V_count = int(input().strip())

    V = list(map(int, input().rstrip().split()))

    result = solve(V)

    fptr.write(str(result) + '\n')

    fptr.close()