#include <bits/stdc++.h>
using namespace std;
const int INF = 1 << 29;
const int MOD = 1073741824;
bool isPowerOfTwo(long long int x) { return x && (!(x & (x - 1))); }
void fastio() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
}
long long binpow(long long a, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1) res = res * a;
    a = a * a;
    b >>= 1;
  }
  return res;
}
const int dx[] = {1, 0, -1, 0, 1, 1, -1, -1};
const int dy[] = {0, -1, 0, 1, 1, -1, -1, 1};
int main() {
  int tc = 1;
  while (tc--) {
    long long int n, d;
    cin >> n >> d;
    long long int ans = 0;
    long long int a[n];
    for (int i = 0; i < (n); i++) {
      cin >> a[i];
    }
    int l = 0, r = 0;
    while (l < n) {
      while (r < n && a[r] - a[l] <= d) r++;
      r--;
      long long int k = r - l;
      ans += 1LL * k * (k - 1) / 2;
      l++;
    }
    cout << ans;
  }
}
