#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int longestConsecutive(vector<int>& nums) {

    unordered_set<int> s(nums.begin(), nums.end());

    if (nums.size() == 0) {
        return 0;
    }

    int longest = 1;

    for (auto it : s) {
        if (s.find(it - 1) == s.end()) {
            int cnt = 1;
            int x = it;

            while (s.find(x + 1) != s.end()) {
                cnt++;
                x = x + 1;
            }

            longest = max(longest, cnt);
        }
    }

    return longest;
}

int main() {
    int n;
    cin >> n;

    vector<int> nums(n);

    for (int i = 0; i < n; i++) {
        cin >> nums[i];
    }

    cout << longestConsecutive(nums);

    return 0;
}