#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#define rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))
#define all(x) (x).begin(),(x).end()
#define inf 1e18

using namespace std;

typedef long long llint;
typedef pair<llint, llint> P;

struct edge{
	llint to, cap, cost, rev;
	edge(){}
	edge(llint a, llint b, llint c, llint d){
		to = a, cap = b, cost = c, rev = d;
	}
};


llint n;
string s;
llint a[2005];
llint S, T;
vector<edge> G[4005];
llint dist[4005];
llint prevv[4005], preve[4005];
llint h[4005];
llint succ[2005][4];


void BellmanFord()
{
	for(int i = 0; i <= T; i++) dist[i] = inf;
	dist[S] = 0, prevv[S] = -1;
	
	bool update = true;
	while(update){
		update = false;
		for(int i = 0; i <= T; i++){
			for(int j = 0; j < G[i].size(); j++){
				if(G[i][j].cap == 0) continue;
				if(dist[G[i][j].to] > dist[i] + G[i][j].cost){
					dist[G[i][j].to] = dist[i] + G[i][j].cost;
					prevv[G[i][j].to] = i;
					preve[G[i][j].to] = j;
					update = true;
				}
			}
		}
	}
}

void Dijkstra()
{
	for(int i = 0; i <= T; i++) dist[i] = inf;
	dist[S] = 0, prevv[S] = -1;
	
	priority_queue< P, vector<P>, greater<P> > Q;
	Q.push( make_pair(0, S) );
	
	llint v, d;
	while(Q.size()){
		d = Q.top().first;
		v = Q.top().second;
		Q.pop();
		if(dist[v] < d) continue;
		for(int i = 0; i < G[v].size(); i++){
			if(G[v][i].cap == 0) continue;
			llint u = G[v][i].to, c = h[v] - h[u] + G[v][i].cost;
			if(dist[u] > d + c){
				dist[u] = d + c;
				prevv[u] = v;
				preve[u] = i;
				Q.push( make_pair(dist[u], u) );
			}
		}
	}
}

void add_edge(llint from, llint to, llint cap, llint cost)
{
	G[from].push_back( edge(to, cap, cost, G[to].size()) );
	G[to].push_back( edge(from, 0, -cost, G[from].size()-1) );
}

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n >> s;
	rep(i, 1, n) cin >> a[i];
	s = "#" + s;
	rep(i, 1, n){
		if(s[i] == 'y') s[i] = '0';
		if(s[i] == 'u') s[i] = '1';
		if(s[i] == 'k') s[i] = '2';
		if(s[i] == 'i') s[i] = '3';
	}
	rep(i, 0, 3) succ[n][i] = n+1;
	for(int i = n-1; i >= 1; i--){
		rep(j, 0, 3) succ[i][j] = succ[i+1][j];
		succ[i][s[i+1]-'0'] = i+1;
	}
	
	S = 2*n+1, T = 2*n+2;
	rep(i, 1, n){
		llint c = s[i]-'0';
		if(c < 3){
			if(succ[i][c+1] <= n) add_edge(i, n+succ[i][c+1], 1, -a[i]);
		}
		else add_edge(i, T, 1, -a[i]);
		if(s[i] == '0') add_edge(S, i, 1, 0);
		
		add_edge(n+i, i, 1, 0);
		if(succ[i][c] <= n) add_edge(n+i, n+succ[i][c], inf, 0);
	}
	add_edge(S, T, inf, 0);
	
	BellmanFord();
	for(int i = 0; i <= T; i++) h[i] = dist[i];
	
	llint f = n, ans = 0;
	while(f > 0){
		Dijkstra();
		if(dist[T] >= inf) break;
		
		llint p = T, flow = f;
		while(prevv[p] != -1){
			flow = min(flow, G[prevv[p]][preve[p]].cap);
			p = prevv[p];
		}
		
		p = T;
		while(prevv[p] != -1){
			G[prevv[p]][preve[p]].cap -= flow;
			G[p][G[prevv[p]][preve[p]].rev].cap += flow;
			p = prevv[p];
		}
		f -= flow;
		ans += (dist[T] + h[T] - h[S]) * flow;
		
		for(int i = 0; i <= T; i++) h[i] += dist[i]; //オーバーフローに注意(?)
	}
	if(f > 0) ans = -1;
	cout << -ans << endl;
	
	return 0;
}