#include<bits/stdc++.h>
using namespace std;
string sss,s[100000];
int main()
{
//	freopen("sort.in","r",stdin);
//	freopen("sort.out","w",stdout);
	int n,m;
	cin>>n>>m;
	cin>>sss;
	int k=0;
	for (int i=0;i<=n-1;i++)
	{
		k++;
		for (int j=i;j<=i+m-1;j++)
		{
			s[k]+=sss[j];
		}
	}
	
	int ans=0;
	for (int i=1;i<=k;i++)
	for (int j=1;j<=k-1;j++)
	{
	if (s[j]>s[j+1]) swap(s[j],s[j+1]),ans++;
	}	
	cout<<ans;
}