#include<bits/stdc++.h>
using namespace std;
ifstream fin("numarare.in");
ofstream fout("numarare.out");
/**
6
1 2 3 4 5 3
*/
int n, a[100005];
int main()
{
    ios::sync_with_stdio(0);
    fin.tie(0);
    fout.tie(0);
    int i,j, st,dr;
    long long sum, ans = 0;
    fin >> n;
    for(i = 1; i <= n; i++)
        fin >> a[i];
    for(i = 1; i < n; i++)
    {
        st = i;
        dr = i + 1;
        sum = a[st] + a[dr];
        while(st >= 1 && dr <= n && a[st] + a[dr] == sum)
            st--, dr++;
        ans += (dr - st - 1) /2;
    }
    fout << ans;
    return 0;
}