#include<bits/stdc++.h>

#define int long long

using namespace std;

const int N=2e5+10;
const int Max=1e9+10;

int a[N];
string s;
int n,m;

int t[N],t1[N];
int maxx=0;
void dfs(int d,int rt){
	if(rt==0||d==5){
		int cnt=0;
		for(int i=1;i<=4;i++){
			cnt+=t[i]*t[i];
		}
		int minn=0x3f3f3f3f;
		for(int i=1;i<=4;i++){
			if(i==1||i==3){
				minn=min(minn,t[i]/2);
			}
			else minn=min(minn,t[i]);
		}
		cnt+=minn*7;
		maxx=max(maxx,cnt);
		return ;
	}
	for(int i=0;i<=rt;i++){
		t[d]+=i;
		dfs(d+1,rt-i);
		t[d]-=i;
	}
	
}

signed main(){
	cin>>n>>m;
	cin>>s;
	for(int i=0;i<n;i++){
		if(s[i]=='k') t[1]++;
		if(s[i]=='r') t[2]++;
		if(s[i]=='o') t[3]++;
		if(s[i]=='d') t[4]++;
	}
	if(m==0){
		int cnt=0;
		for(int i=1;i<=4;i++){
			cnt+=t[i]*t[i];
		}
		int minn=0x3f3f3f3f;
		for(int i=1;i<=4;i++){
			if(i==1||i==3){
				minn=min(minn,t[i]/2);
			}
			else minn=min(minn,t[i]);
		}
		cnt+=minn*7;
		cout<<cnt;
		return 0;
	}
	for(int i=1;i<=4;i++) t1[i]=t[i];
	dfs(1,m);
	cout<<maxx;
	return 0;
}