#include<stdio.h>
#define Nmax 100010

int v[Nmax],i,j,n,last[Nmax],sol;


int calcul (int s, int d)
{
	int rez = 0, i, j, sum = v[s] + v[d];
	
	for( i = s , j = d ; i > 0 && j <= n ; i--, j++ )
		if ( v[i] + v[j] == sum ) rez++;
			else return rez;
	return rez;
}			

int main()
{
	freopen("numarare.in","r",stdin);
	freopen("numarare.out","w",stdout);
	
	scanf("%d",&n);
	
	for ( i = 1 ; i <= n ; i++ )
		scanf("%d",&v[i]);
	
	
	for ( i = 1 ; i < n ; i++ )
		sol += calcul(i,i+1);
		
	printf("%d",sol);
	
	return 0;
}