#include <bits/stdc++.h>

using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
int main(){
    int n,v[9001],i,j,k,nr=0;
    f>>n;
    for(i=1;i<=n;i++)f>>v[i];
    for(i=1;i<=n;i++)
        for(j=1;j<=n-1;j++)
            for(k=j+1;k<=n;k++)if(i!=j&&i!=k&&j<k)
                                  if(v[i]=(v[j]+v[k])/2)nr++;
    g<<nr;



}