#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main(){
    int n;
    cin >> n;
    int a[1000] = {0};
    for(int a_i = 0;a_i < n;a_i++){
       int u; cin >> u;
        a[u] ++;
    }
    
    int ans = 0;
    for (int i = 0; i < 1000 - 1; ++i) {
        ans = max(ans, a[i] + a[i + 1]);
    }
    cout << ans;
    return 0;
}