#include <iostream>
#include <cstdio>
#include <algorithm>
#include <map>
using namespace std;
 
int main() {
	int n, d, x[100005], it;
	long long int cnt1, cnt2, tmp=-1, ans=0, ma=0, mi=0, dif=0;
	const int con=1e9+1;
	map <int, int> m;
	scanf("%d%d", &n, &d);
	for(int i=0; i<n; i++) scanf("%d", &x[i]);
	for(int i=1; i<n; i++) for(int j=x[i-1]; j<x[i]; j++) m[j]=i;
	m[x[n-1]]=n;
	for(int i=0; i<n; i++) {
		if(x[i]+d>=x[n-1]) it=x[n-1];
		else it=x[i]+d;
		dif=m[it]-m[x[i]]+1;
		if(dif>=3) {
			if(m[it]==tmp) continue;
			cnt1=1, cnt2=1;
			for(int j=1; j<=dif; j++) cnt1*=j;
			for(int j=1; j<=dif-3; j++) cnt2*=j;
			ans+=cnt1/(cnt2*6);
			tmp=m[it];
		}
	}
	printf("%lld", ans);
	return 0;
}

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