#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<pii> vpii;
typedef unsigned long long llu;

#define author ayushtomar
#define rf freopen("in.txt", "r", stdin)
#define wf freopen("out.txt", "w", stdout)
#define debug(x) cerr<<#x<<" "<<x<<endl;
#define f first
#define s second
#define mp make_pair
#define pb push_back
int A[1004];
int main()
{
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        int x;
        cin>>x;
        A[x]++;
    }
    int ans=0;
    for(int i=0;i<=1004;i++)
    {
        ans=max(ans, A[i]+A[i+1]);
    }

cout<<ans;
 return 0;
}