#include<iostream>
#define int long long
using namespace std;
const int N=2e5+5,INF=1e9;
char c;
int n,m,d,k,o,r,ans;
int points(int sd,int sk,int so,int sr){
	return sd*sd+sk*sk+so*so+sr*sr+min(min(sr,sd),min(sk/2,so/2))*7;
}
void dfs(int x,int nd,int nk,int no,int nr){
	if(x==0){
		ans=max(ans,points(nd,nk,no,nr));
		return;
	}
	dfs(x-1,nd+1,nk,no,nr);
	dfs(x-1,nd,nk+1,no,nr);
	dfs(x-1,nd,nk,no+1,nr);
	dfs(x-1,nd,nk,no,nr+1);
}
signed main(){
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>c;
		d+=(c=='d'),k+=(c=='k'),o+=(c=='o'),r+=(c=='r');
	}
	dfs(m,d,k,o,r);
	cout<<ans;
	return 0;
}