#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    
    int N;  cin>>N;
    vector<int> ar(101, 0);
    
    for (int i = 0; i < N; ++i) {
        int temp;   cin>>temp;
        ar[temp]++;
    }
    
    int m = 0;
    
    for (int i = 2; i <= 100; ++i) {
        m = max(m, ar[i] + ar[i-1]);
    }
    
    cout<<m<<endl;
    
    return 0;
}