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


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