#include <bits/stdc++.h>
using namespace std;
#define gc getchar_unlocked
#define fo(i,n) for(i=0;i<n;i++)
#define Fo(i,k,n) for(i=k;k<n?i<n:i>n;k<n?i+=1:i-=1)
#define ll long long
#define si(x)	scanf("%d",&x)
#define sl(x)	scanf("%lld",&x)
#define ss(s)	scanf("%s",s)
#define pi(x)	printf("%d\n",x)
#define pl(x)	printf("%lld\n",x)
#define ps(s)	printf("%s\n",s)
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define tr(it, a) for(auto it = a.begin(); it != a.end(); it++)
#define PI 3.1415926535897932384626
typedef pair<int, int>	pii;
typedef pair<ll, ll>	pl;
typedef vector<int>		vi;
typedef vector<ll>		vl;
typedef vector<pii>		vpii;
typedef vector<pl>		vpl;
typedef vector<vi>		vvi;
typedef vector<vl>		vvl;
const int mod = 1000000007;
const int N = 3e5;
vi g[N];
int a[N];
int mpow(int base, int exp); 
void ipgraph(int n, int m);
void dfs(int u, int par);

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int i,n,k,j,x;
	vi cnt(10000, 0);
	cin>>n;
	fo(i, n) cin>>x, cnt[x]++;
	int ans = 0;int pre = -1;
	
	Fo(x, 0, 1000) ans = max(ans, cnt[x]+cnt[x+1]);
	cout<<ans<<endl;
	return 0;
} 

int mpow(int base, int exp) {
	base %= mod;
	int result = 1;
	while (exp > 0) {
	if (exp & 1) result = ((ll)result * base) % mod;
	base = ((ll)base * base) % mod;
	exp >>= 1;
	}
	return result;
}

void ipgraph(int n, int m){
	int i, u, v;
	while(m--){
		cin>>u>>v;
		g[u-1].pb(v-1);
		g[v-1].pb(u-1);
	}
}

void dfs(int u, int par){
for(int v:g[u]){
	if (v == par) continue;
	dfs(v, u);
}
}