#include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <queue>
#include <set>
#include <unordered_set>
#include <complex>
#include <list>
#include <cassert>
#include <chrono>
#include <random>
#include <stack>
#include <iomanip>
#include <fstream>
using namespace std;
#define endl "\n"
#define ll long long
const int INF = 1e9+7;
const int MOD = 1e9+7;
vector<int> construct_range(int m, int k){
return {};
}
bool check(int d1, int d2, int d3, int h1, int h2, int h3){
return (((d1 == h1 && d2 == h2 && d3 == h3) ||
(d1 == h1 && d2 == h3 && d3 == h2) ||
(d1 == h2 && d2 == h1 && d3 == h3) ||
(d1 == h2 && d2 == h3 && d3 == h1) ||
(d1 == h3 && d2 == h1 && d3 == h2) ||
(d1 == h3 && d2 == h2 && d3 == h1)));
}
ll count_triples(vector<int> a){
int n = (int)a.size();
ll cnt = 0;
// if(n <= 100){
// for(int i = 0; i < n; i++){
// for(int j = i; j < n; j++){
// for(int k = j; k < n; k++){
// cnt += check(j-i, k-j, k-i, a[i], a[j], a[k]);
// }
// }
// }
// return cnt;
// }
auto forward = [&](int i){
int first = a[i];
if(i+first>=n) return;
int second = a[i+first];
if(i+first+second>=n) return;
int third = a[i+first+second];
if(third == first+second){
cnt++;
}
};
auto backfor = [&](int i){
int first = a[i];
if(i-first<0) return;
int second = a[i-first];
if(i+second>=n) return;
int third = a[i+second];
if(first <= second && second <= third) return;
if(first >= second && second >= third) return;
if(third == first+second){
cnt++;
}
};
auto backward = [&](int i){
int first = a[i];
if(i-first<0) return;
int second = a[i-first];
if(i-first-second<0) return;
int third = a[i-first-second];
if(first == third+second){
cnt++;
}
};
for(int i = 0; i < n; i++){
forward(i);
backfor(i);
backward(i);
}
return cnt;
}
