#include <bits/stdc++.h>   using namespace std;   const int sizes = 200001;   int main() {     long long int i, j, k, l, m, n, o, p, q, r, s, t, a[sizes], b[sizes],         booked[1001];     cin >> n;     o = 0;     for (i = 0; i < n; i++) {       cin >> a[i];       o = max(o, a[i]);     }     sort(a, a + n);     memset(b, -1, sizeof(b));     for (i = 0; i < n; i++) {       b[a[i]] = i;     }     long long int ans = 1;     for (i = 2 * 1; i <= 2 * o; i++) {       memset(booked, 0, sizeof(booked));       p = 0;       for (j = 0; j < n; j++) {         if (booked[j] == 0) {           if ((i - a[j] > 0) && b[i - a[j]] != -1) {             if (booked[b[i - a[j]]] == 0 && j != b[i - a[j]]) {               booked[j] = 1;               booked[b[i - a[j]]] = 1;               p++;             }           }         }       }       ans = max(ans, p);     }     cout << ans << endl;     return 0;   }   