#include<bits/stdc++.h>
using namespace std;
#define _              ios_base::sync_with_stdio(0);cin.tie(0);
#define pb             emplace_back
#define mp             make_pair
#define F              first
#define S              second
#define rep(i, x)      for (__typeof(x) i = 0; i < x; i ++)
#define repp(i, x, y)  for (__typeof(x) i = x; i < y; i ++)
#define all(a)         (a).begin(),(a).end()
#define endl           '\n'
#define DB(x)          cerr << #x << " is " << x << endl;
#define INF            1000000007
typedef long long          ll;
typedef vector<int>        vi;
typedef set<int>           si;
typedef pair<int, int>     ii;
typedef vector<ii>        vii;

int main(){ _
    int n; cin >> n;
    vi v(100, 0);
    int t;
    rep(i, n) cin >> t, v[t]++;
    int i = 1, m = 1;
    while (i<99){
        if (v[i] > 0) m = max(m, v[i]);
        if (v[i] > 0 && v[i-1]>0) m = max(m, v[i]+v[i-1]);
        if (v[i] > 0 && v[i+1]>0) m = max(m, v[i]+v[i+1]);
        i++;
    }
    cout << m;
}