#include <bits/stdc++.h>
#define int long long
using namespace std;

int n, m, ans;
string s;
int t[5];
map <char, int> mp;
char pm[5];

void dfs(int u)
{
	if(u == m+1)
	{
		int res = 0;
		for(int i=1; i<=4; i++)
			res += t[i]*t[i];
		res += 7 * min({t[1], t[2]/2, t[3]/2, t[4]});
		ans = max(ans, res);
		return ;
	}
	for(int i=1; i<=4; i++)
		t[i] ++, dfs(u+1), t[i] --;
}

signed main()
{
	mp['d'] = 1, mp['k'] = 2, mp['o'] = 3, mp['r'] = 4;
	pm[1] = 'd', pm[2] = 'k', pm[3] = 'o', pm[4] = 'r';
	cin >> n >> m >> s;
	for(char c:s)
		t[mp[c]] ++;
	dfs(1);
	cout << ans;
	return 0;
 }