#include <fstream>

using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
int n,v[9001],i,j,v2[7001],sum;
int main()
{
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
        v2[v[i]]++;
    }
    for(i=1;i<n;i++)
    {
        for(j=i+1;j<=n;j++)
        {
            if(v[i]%2==v[j]%2)
            {
                sum+=v2[(v[i]+v[j])/2];
                if(v[i]==v[j])
                {
                    sum=sum-2;
                }
            }
        }
    }
    g<<sum;
    return 0;
}