#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){

    ll N, ans=0;
    cin >> N;
    vector<int> A(N+1);

    vector<vector<int>> S(N+1, vector<int>(2001)), T(N+2, vector<int>(2001));

    for (int i=1; i<=N; i++){
        cin >> A[i];
        S[i][A[i]]++;
        T[i][A[i]]++;
    }

    for (int i=1; i<=N; i++) for (int j=0; j<=2000; j++) S[i][j] += S[i-1][j];
    for (int i=N; i>=1; i--) for (int j=0; j<=2000; j++) T[i][j] += T[i+1][j];

    for (int i=1; i<=N; i++){
        for (int j=i+1; j<=N; j++){
            if (A[j]-10>=0 && A[i]+1<=2000 && A[i]-A[j] >= 1) ans += S[i-1][A[j]-10] * T[j+1][A[i]+1];
        }
    }

    cout << ans << endl;

    return 0;
}