#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,num;
    cin >> n;
    int *freq=(int*)calloc(100,sizeof(int));
    for(int i=0;i<n;i++)
        {
        cin>>num;
        freq[num]++;
    }
    int max=0;
    if(freq[1]+freq[2]>max) max=freq[1]+freq[2];
    if(freq[99]+freq[98]>max) max=freq[99]+freq[98];
    for(int i=2;i<=98;i++){
        if(freq[i-1]+freq[i]>max) max=freq[i-1]+freq[i];
        if(freq[i]+freq[i+1]>max) max=freq[i]+freq[i+1];
    }
    cout<<max;
    return 0;
}