#include <cstdio>
#include <algorithm>
#define Nmax 9001

using namespace std;

int v[Nmax],N;

void citire()
{
    scanf("%d",&N);
    for(int i=0; i<N; i++)
        scanf("%d",v+i);
}


void solve()
{
    int nr = 0;

    sort(v,v+N);
    for(int i=0; i<N-1; i++)
        for(int j=i+1; j<N; j++)
        {
            int m = (v[i] + v[j]) >> 1;
            for(int k = 0; k<N; k++)
                if(v[k] == m && k!=i && k!=j)
                    nr++;
        }

    printf("%d\n",nr);
}

int main()
{
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    citire();
    solve();
}