#include<stdio.h>
int main(){
	int n,v[9000],i,j,k;
	long long s=0;
	freopen("medie.in","r",stdin);
	freopen("medie.out","w",stdout);
	scanf("%d",&n);
	for(i=0;i<n;++i)
		scanf("%d",&v[i]);
	for(i=0;i<n;++i)
		for(j=0;j<n-1;++j)
			for(k=j+1;k<n;++k)
				if(v[i]==(v[j]+v[k])/2 && k!=i && i!=j && ((v[j]+v[k])%2)==0)
					s++;
	printf("%lld\n",s);
	fclose(stdin);
	fclose(stdout);
	return 0;
}