#include <bits/stdc++.h>
using namespace std;
long long const M = 1000000007;
double const pi = acos(-1);
long long const inf = 2e18;
long long const N = 200001;
long long comb(long long n) {
  if (n <= 0) return 0;
  return (n * (n - 1)) / 2;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long i, j, t, n, d, ans = 0, curr, prev = 0;
  cin >> n >> d;
  vector<long long> a(n);
  for (i = 0; i < n; i++) cin >> a[i];
  for (curr = 2; curr < n;) {
    while (curr < n && a[curr] - a[prev] <= d) {
      ans += comb(curr - prev);
      curr++;
    }
    if (a[curr] - a[prev] > d) prev++;
  }
  cout << ans << "\n";
  return 0;
}
