#include <bits/stdc++.h>
using namespace std;
long long n, d, ans = 0;
vector<long long> a;
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> d;
  while (n--) {
    long long temp;
    cin >> temp;
    a.push_back(temp);
  }
  for (long long i = 0; i < a.size(); i++) {
    long long idx = upper_bound(a.begin(), a.end(), a[i] + d) - a.begin();
    idx--;
    if (idx > i + 1) ans += ((idx - i) * (idx - i - 1)) / 2;
  }
  cout << ans << endl;
  return 0;
}
