#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;
}

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