//#pragma G++ optimize ("O2")
//#pragma GCC optimize("O2")
#include <bits/stdc++.h>
using namespace std;
string s,a[50005],b[50005];
int m,n;
int main()
{
//    freopen("sort.in","r",stdin);
//    freopen("sort.out","w",stdout);
	scanf("%d %d",&n,&m);
	cin>>s;
	for(int i=0;i<=n-m+1;i++)
	  for(int j=1;j<=m;j++)
	    if((i+j-1)<=n-1)
	    {
	      a[i+1]+=s[i+j-1];
		}
	for(int i=1;i<=n;i++)
	  b[i]=a[i];
    sort(a+1,a+n+1);
//    for(int i=1;i<=n;i++)
//      cout<<a[i]<<endl;
    int ans=0;
    for(int i=1;i<=n;i++)
      if(a[i]!=b[i])
        ans++;
    printf("%d",ans);
	return 0;
}