#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    ll N; cin >> N;
    vector<ll>A(N);
    ll Max = -1;
    for (ll i = 0; i < N; i++) {
        cin >> A[i];
        Max = max(Max, A[i]);
    }
    ll ans = 0;
    for (ll k = 1; k <= Max; k++) {
        vector<vector<ll>>dp(N, vector<ll>(4, 0));
        vector<vector<ll>>C(Max + 1, vector<ll>(4, 0));
        dp[N - 1][3] = 1;
        C[A[N - 1]][3]++;
        for (ll i = N - 2; i >= 0; i--) {
            dp[i][3] = 1;
            if (0 <= A[i] + k + 1 && A[i] + k + 1 <= Max) dp[i][2] = C[A[i] + k + 1][3];
            if (0 <= A[i] - k && A[i] - k <= Max) dp[i][1] = C[A[i] - k][2];
            if (0 <= A[i] + 10 + k && A[i] + 10 + k <= Max) dp[i][0] = C[A[i] + 10 + k][1];
            for (ll j = 0; j < 3; j++) {
                C[A[i]][j] += dp[i][j];
            }
        }
        for (ll i = 0; i < N; i++) {
            ans += dp[i][0];
        }
    }
    cout << ans << endl;
}