#include <cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
int v[30005],i,j,n,c;
int Numarare()
{
    for(i=1;i<=n;i++)
        for(j=i+1;j<=n;j++)
            if(binary_search(v+1,v+n+1,v[i]+v[j]))
                c++;
}
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    Numarare();
    printf("%d",c);
    return 0;
}