#include<cstdio>
using namespace std;

FILE *f;
FILE *g;

int n,a[7001],i,j,k;
int main()
{
	f=fopen("medie.in","r");
	g=fopen("medie.out","w");
	fscanf(f,"%d\n",&n);
	for(i=1;i<=n;i++)
		fscanf(f,"%d\n",&a[i]);
	for(i=1;i<=n;i++)
		for(j=1;j<=n;j++)
			for(k=1;k<=n;k++)
				if(k!=j&&k!=i&&j!=i&&a[i]==(a[j]+a[k])/2&&(a[j]+a[k])%2==0)
					a[0]++;
	fprintf(g,"%d\n",a[0]/2);
	fclose(f);
	fclose(g);
	return 0;
}