#include<iostream>
#include<cstring>
using namespace std;
#define int long long
int maxn=0;
int dfs(int n,int a,int b,int c,int d){
	if(n==0){
		int t=a*a+b*b+c*c+d*d+7*min(a/2,min(b/2,min(c,d)));
		maxn=max(maxn,t);
		return t;
	}
	int t=dfs(n-1,a+1,b,c,d);
	t=max(t,dfs(n-1,a,b+1,c,d));
	t=max(t,dfs(n-1,a,b,c+1,d));
	t=max(t,dfs(n-1,a,b,c,d+1));
	return t;
}
using namespace std;
char s[100001];
int a,b,c,d,t,g;
signed main(){
	cin>>t>>g; 
	cin>>s;
	for(int i=0;i<t;i++){
		if(s[i]=='d'){
			c++;
		}
		if(s[i]=='k'){
			a++;
		}
		if(s[i]=='r'){
			d++;
		}
		if(s[i]=='o'){
			b++;
		}
	}
	cout<<dfs(g,a,b,c,d);
	return 0;
} 
//6 4 2 3
//36
//16
//4
//9





















//(x1+a)^2+(x2+b)^2+(x3+c)^2+(x4+d)^2+min((x1+a)/2,(x2+b)/2,)