#include <iostream>

 #include <cstdio>

 #include <fstream>

 #include <algorithm>

 #include <cmath>

 #include <deque>

 #include <vector>

 #include <queue>

 #include <string>

 #include <cstring>

 #include <map>

 #include <stack>

 #include <set>

 #define LL long long

 #define eps 1e-8

 #define INF 0x3f3f3f3f

 #define MAXN 200005

 using namespace std;

 int a[];

 bool vis[];

 int main()

 {

 #ifndef ONLINE_JUDGE

     freopen("in.txt", "r", stdin);

     //freopen("out.txt", "w", stdout);

 #endif // OPEN_FILE

     int n;

     scanf("%d", &n);

     for(int i = ; i <= n; i++){

         scanf("%d", &a[i]);

     }

     int ans = ;

     for(int i = ; i <= n; i++){

         for(int j = ; j <= i - ; j++){

             if(!vis[a[i] - a[j] + MAXN]) continue;

             ans++;

             break;

         }

         for(int j = ; j <= i; j++){

             vis[a[i] + a[j] + MAXN] = true;

         }

     }

     printf("%d\n", ans);

 }