#include <iostream>
#include <string>
using namespace std;
 
struct data
{
	int leng;
	long at[25];
} typedef data;
 
data arr[300005];
 
int main ()
{
	long n, k;
	cin>>n>>k;
 
	//Khoi tao;
	arr[0].leng=0;
	for (int i=1; i<=20; i++)
		arr[0].at[i]=0;
 
	for (long i=1; i<=n; i++)
	{
		string tmp;
		cin>>tmp;
		int len = tmp.length();
		arr[i].leng = len;
		for (int j=2; j<=20; j++)
			arr[i].at[j] = arr[i-1].at[j];
		arr[i].at[len]++;
	}
	long long pair = 0;
	for (long i=1; i<=n; i++)
	{
		int len = arr[i].leng;
		if (i>k)
		{
			pair += (arr[i].at[len] - arr[i-k-1].at[len] - 1);
		}
		else
		{
			pair += (arr[i].at[len] - arr[0].at[len] - 1);
		}
	}
	cout<<pair;
	return 0;
}