#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]);
// if(check(j-i, k-j, k-i, a[i], a[j], a[k])) cout << a[i] << " " << a[j] << " " << a[k] << endl;
}
}
}
return 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(third == first+second){
cnt++;
// cout << first << " " << second << " " << third << endl;
}
};
// 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++;
// // cout << first << " " << second << " " << third << endl;
// }
// };
for(int i = 0; i < n; i++){
backfor(i);
}
return cnt;
}
