#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int counts[110];

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    int n;
    cin>>n;
    for(int i=0;i<=100;i++)counts[i]=0;
    for(int i=0;i<n;i++){
        int t;
        cin>>t;
        counts[t]++;
    }
    int m=-1;
    for(int i=2;i<=100;i++){
        m=max(counts[i]+counts[i-1],m);
        
        
    }
    cout<<m<<endl;
    return 0;
    
}