#include <iostream>
using namespace std;

int main(){
    int n, temp; cin >> n;
    int arr[100] = {0};
    for(int i = 0;i < n;i++){
        cin >> temp;
        arr[temp - 1]++;
    }
    int max = arr[0] + arr[1];
    for(int i = 2;i < 100;i++) max = max > arr[i] + arr[i - 1] ? max : arr[i] + arr[i - 1];
    cout << max << endl;
    return 0;
}