# include <cstdio>

using namespace std;

int n, i, j, k, ct;
int a[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++)
        for (j = 1; j <= n; j++)
            for (k = n; k >= j + 1; k--)
            if (i != j && i != k && (a[i] == (a[j] + a[k]) / 2) && (a[j] + a[k]) % 2 == 0) 
                  ct++;
                  
    printf("%d",ct);
    
return 0;
}