#include<fstream>
using namespace std;
int a[100010];

int main(void){
    ifstream fin("numarare.in");
    ofstream fout("numarare.out");
    int n,i,nr,i1,j1,k;
    fin>>n; nr=n-1;
    for(i=1;i<=n;++i)fin>>a[i]; fin.close();
    for(i=1;i<n;++i)
             if(a[i-1]+a[i+2]==a[i]+a[i+1]){
                  k=a[i]+a[i+1]; i1=i-1; j1=i+2;
                  while(a[i1]+a[j1]==k && i1>0 && j1<=n){++nr; --i1; ++j1; }                                                                                                         
                                       }
    fout<<nr; fout.close();
 return 0;   
}