# include <cstdio>

using namespace std;

int n, i, j, ct;
int a[9005], frecv[9005];
int main()
{
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    
    scanf("%d",&n);
    
    for (i = 1; i <= n; i++)
    scanf("%d",&a[i]);
    
    for (i = 1; i <= n; i++)
    {
        scanf("%d",&a[i]);
        for (j = i - 1; j >= 1; j--)
        if ((a[i] + a[j]) % 2 == 0)
                  frecv[(a[i] + a[j]) / 2]++; 
        }
    
    for (i = 1; i <= n; i++)
        ct += frecv[a[i]];
                  
    printf("%d",ct);
    
return 0;
}