#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))
a=sorted(a)
count=1
j=0
for i in range(len(a)-1):
    if abs(a[i]-a[i+1])<=1 and abs(a[j]-a[i+1])<=1:
       count+=1
    else:
        j+=1
print count