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

typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> ii;

#define fill(a,x) memset(a,x,sizeof(a)) 
#define pb push_back
#define sz(x) (int)x.size()
#define all(x) x.begin(),x.end() 
#define F first
#define S second
#define FOR(i,a,b) for(int i = a; i<=b; ++i)
#define NFOR(i,a,b) for(int i = a; i>=b; --i)
#define fast ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0)
const ll INF = 1e18;
const int mod = 1e9+7;
const int N = 1e5+10; 

int main(){
  fast;
  int n;cin >> n;
  map<int,int> M;
  FOR(i,0,n-1){
    int x;cin >> x;
    M[x]++;
  }
  int ans = 0;
  int last = 0;
  int lol = 0;
  for(auto it : M){
    if(lol == it.F - 1)ans = max(ans,it.S + last);
    ans = max(ans,it.S);
    last = it.S;lol = it.F;
  }
  cout << ans << "\n";
  return 0;
}