#include <bits/stdc++.h>

using namespace std;

int a[100001];
int u[100001];


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n;
    cin >> n;
    for (int i = 1;i <= n;i ++) {
        cin >> a[i];
        u[a[i]] ++;
    }
    int ans = 0;
    for (int i = 1;i <= 1000;i ++) {
        ans = max (ans, u[i] + u[i + 1]);
    }
    cout << ans;
    return 0;
}