#include <bits/stdc++.h>

using namespace std;
ifstream fin("numarare.in");
ofstream fout("numarare.out");
typedef long long ll;
ll n,v[100005],z[100005],ans;
int main()
{
    ios_base::sync_with_stdio(false);
    fin.tie(0);
    fin>>n;
    for(int i=1;i<=n;i++)
        fin>>v[i];
    for(int i=1;i<n;i++)
    {
        if(i>2)
            z[i]=min(z[i-2],z[i-1]-1);
        while(i+z[i]+1<=n&&i-z[i]>=1&&v[i-z[i]]+v[i+z[i]+1]==v[i]+v[i+1])
            z[i]++;
        ans+=z[i];
    }
    fout<<ans;
    return 0;
}