#include<stdio.h>
int main(){
	int a[102]={0};
	int flag[102]={0};
	int n;
	scanf("%d",&n);
	int i=1;
	while(i<=n){
		scanf("%d",&a[i]);
		i++;
	}
	int u=1;
	while(u<=n-1){
		int z=u+1;
		while(z<=n){
			if(a[u]>a[z]){
				int num=a[u];
				a[u]=a[z];
				a[z]=num;
			}
			z++;
		}
		u++;
	}
	int NUM=0;
	int x=3;
	while(x<=n){
		int y=1;
		while(y<=x-2){
			int k=y+1;
			while(k<=x-1){
				if(a[y]+a[k]==a[x]&&flag[x]==0){
					NUM++;
					flag[x]=1;
				}
				k++;
			}
			y++;
		}
		x++;
	}
	printf("%d",NUM);
	return 0;
}