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

typedef long long ll;
typedef double ld;
typedef pair<ll,ll> pl;

#define sl(x) scanf("%d",&x)
#define pl(x) printf("%lld\n",x)
#define sf(x) sort(x.begin(),x.end(),func)
#define s(x) sort(x.begin(),x.end())
#define all(v) v.begin(),v.end()
#define rs(v) { s(v) ; r(v) ; }
#define r(v) {reverse(all(v));}
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define f(i,n) for(int i=0;i<n;i++)
#define rep(i,a,b) for(int i=a;i<=b;i++)

const ll mod = 1000000007;
const ll inf = (ll)5e18;
const ld eps = 1e-12;
const ll N = 2000005;
const ll LOGN = 19;
const ld PI = 3.14159265358979323846;
ll mul(ll a, ll b, ll m = mod) { return (ll)(a * b) % m;}
ll add(ll a, ll b, ll m = mod) { a += b; if(a >= m) a -= m; if(a < 0) a += m; return a;}
ll power(ll a, ll b, ll m = mod) { if(b == 0) return 1; if(b == 1) return (a % m); ll x = power(a, b / 2, m); x = mul(x, x, m); if(b % 2) x = mul(x, a, m); return x;}
ll n, a[N];
int main()
{
    ios_base::sync_with_stdio(0);
    cin >> n;
    map < ll , ll > m;
    f(i, n) cin >> a[i];
    f(i, n) m[a[i]]++;
    sort(a, a + n);
    ll ans = 0;
    for(auto it = m.begin(); it != m.end(); it++)
    {
        ll no = it -> F;
        ll xx = it -> S;
        no++;
        if(m.find(no) != m.end())
        {
            ans = max(ans, xx + m[no]);
        }
        ans = max(ans, xx);
    }
    cout << ans << "\n";
    return 0;
}