#include <fstream>
using namespace std;
ifstream cin("numarare.in");
ofstream cout("numarare.out");
int main(){
    int n;
    cin>>n;
    int l1[n], d[n];
    for(int x = 0;x<n;x++)
        cin>>l1[x];
    for(int x = 0, l = 0, r = -1;x<n;x++){
        int k;
        if(x > r){
            k = 0;
        }else k = min(d[l + r - x + 1], r - x + 1);
        while((x - k) && ((x + k) < n) && ((l1[x - k - 1] + l1[x + k]) == (l1[x - 1] + l1[x])))
            k++;
        d[x] = k--;
        if((x + k) > r){
            l = x - k - 1;
            r = x + k;
        }
    }
    long long int res = 0;
    for(int x = 0;x<n;x++)
        res += d[x];
    cout<<res<<endl;
    return 0;
}