#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const long long INF = 1e18;
const int MAXN = 1e5 + 5;
long long i, j, m, n, k, t, d;
long long ans;
long long x[MAXN];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> d;
  for (i = 1; i <= n; i++) {
    cin >> x[i];
  }
  for (i = 1; i <= n; i++) {
    long long low = i + 2, high = n, mid, ok = -1;
    while (low <= high) {
      mid = (low + high) / 2;
      if (x[mid] - x[i] <= d) {
        ok = mid;
        low = mid + 1;
      } else {
        high = mid - 1;
      }
    }
    if (ok == -1) continue;
    ans += (ok - i) * (ok - i - 1) / 2;
  }
  cout << ans;
  return 0;
}
