#include <fstream>

using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
int v[7007];
int main()
{
    int n,i,k,j,c=0;
    f>>n;
    for (i=1;i<=n;++i) f>>v[i];

    for (i=1;i<=n;++i)
    {
        for (j=1;j<=n;++j)
        {
            if (j!=i)
                for (k=j+1;k<=n;++k)
                {
                    if (v[i]==(v[j]+v[k])/2 && i!=k && (v[j]+v[k])%2==0)
                        {
                            c++;
                        }
                }
        }
    }
    g<<c;
    return 0;
}