#include<bits/stdc++.h>
#define INF 9999999
#define INFN -999999999

#define ll long long int
#define ull unsigned long long int

#define si(n) scanf("%d",&n);
#define sf(n) scanf("%f",&n);
#define sll(n) scanf("%lld",&n);
#define sull(n) scanf("%llu",&n);
#define schar(n) scanf("%c",&n);
#define sstr(n) scanf("%s",&n);
 
#define pi(n)  printf("%d",n);
#define pll(n)  printf("%lld",n);
#define pull(n)  printf("%llu",n);
#define pf(n)  printf("%f",n);
#define pchar(n) printf("%c",n);
#define nl printf("\n");
using namespace std;


int main()
{
    int k,res=0,temp=0;
    int i,j,n;
    int a[1000];
    si(n);
    bool flag=true;
    
    for(i=0;i<n;i++)
        si(a[i]);
    
    sort(a,a+n);
    
    for(i=0;i<n-1;i++)
    {
        if(a[i]==a[i+1])
            temp++;
        
        else if( a[i]+1==a[i+1] && flag)
        {
            temp++;
            flag=false;
        }
        
        else
        {
            temp++;
            res=max(res,temp);
            temp=0;
            flag=true;
        }
    }
    
    if(a[n-1]==a[n-2])
        temp++;
    if(!flag&& a[n-1]==a[n-2]+1)
        temp++;
    
        
        
    res=max(res,temp);
    
    pi(res);nl;
   return 0;
}