// 嘘解法 (TLE)
// 愚直 O(N^4) を QCFium法 で定数倍高速化

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);

    int N;
    cin >> N;
    vector<int> A(N);
    for (int i = 0; i < N; i++) { cin >> A[i]; }

    ll ans = 0;
    for (int i1 = 0; i1 < N - 3; i1++) {
        for (int i2 = i1 + 1; i2 < N - 2; i2++) {
            int n = A[i2] - A[i1] - 10;
            if (n <= 0) { continue; }
            for (int i3 = i2 + 1; i3 < N - 1; i3++) {
                if (A[i3] != A[i2] - n) { continue; }
                for (int i4 = i3 + 1; i4 < N; i4++) {
                    if (A[i4] != A[i3] + (n + 1)) { continue; }
                    ans++;
                }
            }
        }
    }
    cout << ans << '\n';

    return 0;
}