#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vb> vvb;
typedef pair<int,int> pii;
typedef vector<pii> vpii;
typedef vector<vpii> vvpii; 
typedef set<int> si;
typedef map<int,int> mii;
typedef priority_queue<int> pqi;
typedef priority_queue<pii> pqpii;
#define fir first
#define sec second
#define pb push_back
#define mp make_pair
#define sz(x) x.size()
#define rep(i,n) for(int i=0;i<n;i++)
#define fo(i,a,b) for(int i=a;i<b;i++)
#define fd(i,a,b) for(int i=a;i>b;i--) 
#define tr(it,x) for(it=x.begin();it!=x.end();it++)
#define rtr(it,x) for(it=x.rbegin();it!=x.rend();it++)
#define fast_io ios_base::sync_with_stdio(0);
#define accuracy  int precision = numeric_limits<double>::digits10;

int main() {
    fast_io;
    accuracy;

    int n; cin >> n;
    map<int,int> x;

    rep(i,n) {
    	int temp; cin >> temp;
    	if(x.count(temp) == 0) x[temp] = 1;
    	else x[temp]++;
    }

    int ans = INT_MIN,ans2 = INT_MIN;

    map<int,int>::iterator it;
    tr(it,x) {
    	map<int,int>::iterator it1;
    	it1 = it; it1++;
    	if(it1 != x.end()) {
    		if(it1->fir - it->fir == 1) {
    			ans = max(ans,it1->sec+it->sec);
    		}
    	}
    }

    tr(it,x) {
    	ans2 = max(ans2,it->sec);
    }
    cout << max(ans,ans2) << endl;   
}