# include <stdio.h>
int main(void)
{
	int number[100],n,i,k,l,sum,cnt=0;//cnt为计数器 
	int v[100]={0};//判断是否重复 
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d",&number[i]);
	}
	for(i=0;i<n;i++)
	{	
		for(k=i+1;k<n;k++)
		{
			sum=number[i]+number[k];
			for(l=k+1;l<n;l++)
			{
				if(sum==number[l]&&v[k]==0)
				{
				v[k]=1;
				cnt++; 
				} 
			}
		}
	}
	printf("%d",cnt);
}