#include <bits/stdc++.h>
using namespace std;
template <class T>
int getbit(T s, int i) {
  return (s >> i) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
template <class T>
int cntbit(T s) {
  return __builtin_popcount(s);
}
template <class T>
inline T gcd(T a, T b) {
  T r;
  while (b != 0) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
long long n, a[100005], d, res;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> d;
  for (long long i = 1, _b = n; i <= _b; i++) cin >> a[i];
  for (long long i = 1, _b = n; i <= _b; i++) {
    long long tmp = upper_bound(a + i, a + n + 1, a[i] + d) - a;
    tmp -= i + 1;
    if (tmp >= 2) {
      res += tmp * (tmp - 1) / 2;
    }
  }
  cout << res;
  return 0;
}
