#include <iostream>
#include <unordered_set>
#include <algorithm>
using namespace std;
typedef long long int LLI;
 
int main() {
    int N;
    cin >> N;
    unordered_set<LLI> s, n;
    LLI list[1000];
    for (int i = 0; i < N; i++) {
        cin >> list[i];
        n.emplace(list[i]);
    }
    // 두 개의 합을 미리 저장한 후 그걸 순회하며 탐색
    sort(list, list + N);
    for (int i = 0; i < N; i++) {
        for (int j = i; j < N; j++) {
            s.emplace(list[i] + list[j]);
        }
    }
    for (int i=N-1; i>=0; i--) {
        // list[i] = n? + s?
        for (int j = i-1; j>=0; j--) {
            LLI t = list[i];
            if (s.count(t - list[j])) {
                cout << t;
                return 0;
            }
        }
    }
}
 

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