#include<stdio.h>

int n,i,j,var,nrp;
short int v[7001];

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

 scanf("%d",&n);
 for(i=1;i<=n;i++) {scanf("%d",&var);
		    v[var]++;}


 for(i=1;i<=7000;i++)
 if(v[i]>=1)
 {var=i*2;
 for(j=1;j<i;j++)
 if(v[j]>=1)
 if(v[var-j]>=1)
 nrp+=v[j]*v[var-j]*v[i];

 var=v[i]; nrp+=var*(var-2)*(var-1)/2;}

 printf("%d",nrp);}