#include<bits/stdc++.h>
using namespace std;
#define int long long
int c[10];
int n,m;
int ans = 0;
void check()
{
	int sum = 0;
	int mi = 1e5;
	for(int i = 1;i <= 4;i++)
	{
		if(i == 2 || i == 3) mi = min(mi,c[i] / 2);
		else mi = min(mi,c[i]);
		sum += c[i] * c[i];
	}
	sum += mi * 7;
	ans = max(ans,sum);
}
void dfs(int pos)
{
	if(pos > m)
	{
		check();
		return;
	} 
	for(int i = 1;i <= 4;i++)
	{
		c[i]++;
		dfs(pos + 1);
		c[i]--;
	}
}
signed main()
{
	cin >> n >> m;
	for(int i = 1;i <= n;i++)
	{
		char ch;
		cin >> ch;
		if(ch == 'd') c[1]++;
		else if(ch == 'k') c[2]++;
		else if(ch == 'o') c[3]++;
		else c[4]++;
	}
	dfs(1);
	cout << ans << endl;
	return 0;
}