#include <bits/stdc++.h>   using namespace std;   void fastio() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);   }   long long fre[1000000];   int32_t main() {     fastio();     long long n;     cin >> n;     long long a[n];     for (long long i = 0; i < n; i++) cin >> a[i];     sort(a, a + n);     for (long long i = 0; i < n; i++) {       for (long long j = i + 1; j < n; j++) {         fre[a[i] + a[j]]++;       }     }     long long ans = 0;     for (long long i = 0; i < 1000000; i++) {       ans = max(ans, fre[i]);     }     cout << ans;   }   