//N^2
#include<stdio.h>

const int N=100001;

int n,v[N],rez;

void Read(){
    scanf("%d",&n);

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

void Verify( int st, int dr){
    while( st && dr<=n && v[st]+v[dr]==v[st+1]+v[dr-1] )
        rez++,st--,dr++;
}

void Solve(){
    for( int i=1; i<n; ++i)
        Verify(i,i+1);
}

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

	Read();

	Solve();

	printf("%d\n",rez);

	return 0;
}