#include <cstdio>
int n,a[7005];
int main (){
	int i,i2,i3,k=0;
	freopen("medie.in","r",stdin);
	freopen("medie.out","w",stdout);
	scanf("%d", &n);
	for(i=0;i<n;++i){
		scanf("%d", &a[i]);
	}
	for(i=0;i<n;++i){
		for(i2=0;i2<n;++i2){
			for(i3=i2+1;i3<n;++i3){
				if(i!=i2 && i2!=i3 && i!=i3 && (a[i]+a[i2])/2==a[i3])
					++k;
			}
		}
	}
	printf("%d",k);
}