#include <bits/stdc++.h>
using namespace std;
template <class T>
void max_self(T &a, const T &b) {
  if (a < b) a = b;
}
template <class T>
void min_self(T &a, const T &b) {
  if (a > b) a = b;
}
const int INF = 1e9 + 7;
const double PI = acos(-1.0);
const double EPS = (1e-9);
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int N, d;
  long long cnt = 0;
  cin >> N >> d;
  vector<int> pos(N);
  for (int &ele : pos) cin >> ele;
  for (auto itr = pos.begin(); itr != pos.end(); ++itr) {
    auto lim = upper_bound((pos).begin(), (pos).end(), *itr + d);
    int len = distance(itr, lim) - 1;
    cnt += (long long)len * (len - 1) / 2;
  }
  cout << cnt << "\n";
  return 0;
}
