#include<bits/stdc++.h>
#define ll   long long
using namespace std;
ll n,m,a[1000];
ll dfs(ll x){
	ll ans=a['d']*a['d']+a['k']*a['k']+a['o']*a['o']+a['r']*a['r']
		+7*min(min(a['d'],a['r']),min(a['k'],a['o'])/2);
	if(x==0){
		return ans;
	}
	a['d']++;
	ans=max(ans,dfs(x-1));
	a['d']--;
	a['k']++;
	ans=max(ans,dfs(x-1));
	a['k']--;
	a['o']++;
	ans=max(ans,dfs(x-1));
	a['o']--;
	a['r']++;
	ans=max(ans,dfs(x-1));
	a['r']--;
	return ans;
}
int main(){
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		char x;
		cin>>x;
		a[x]++;
	}
	cout<<dfs(m);
	return 0;
}