#include<iostream>
#include<algorithm>
#include<unordered_map>
using namespace std;
#define MAXN 10005

long long n, a[MAXN], ans = 0;
unordered_map<long long, long long> mp[MAXN];

int main() {
    cin >> n;
    for(int i = 1; i <= n; i ++) cin >> a[i];
    sort(a + 1, a + n + 1);
    for(int i = 2; i <= n; i ++) 
        for(int j = 1; j < i; j ++) {
        	if(!mp[j][a[i] - a[j]]) mp[j][a[i] - a[j]] = 1;
        	mp[i][a[i] - a[j]] = mp[j][a[i] - a[j]] + 1, 
            ans = max(ans, mp[i][a[i] - a[j]]);
		}
    cout << ans << "\n";
    return 0;
}

为什么会 RE 35pts