ll@n;
string@s;
ll@v[n];
minCostFlow<ll,ll>f;
f.malloc(n+1);
f.init(n+1);
ll Y=n,U=n,K=n,I=n;
rrep(i,n){
	if(s[i]=='y'){
		if(Y<n) f.addEdge(i,Y,n,0);
		if(U<n) f.addEdge(i,U,1,1d9-v[i]);
		Y=i;
	}
	if(s[i]=='u'){
		if(U<n) f.addEdge(i,U,n,0);
		if(K<n) f.addEdge(i,K,1,1d9-v[i]);
		U=i;
	}
	if(s[i]=='k'){
		if(K<n) f.addEdge(i,K,n,0);
		if(I<n) f.addEdge(i,I,1,1d9-v[i]);
		K=i;
	}
	if(s[i]=='i'){
		if(I<n) f.addEdge(i,I,n,0);
		f.addEdge(i,n,1,1d9-v[i]);
		I=i;
	}
}
ll fres,cres=4d9*n;
if(Y<n){
	f.addEdge(Y,n,n,4d9);
	f.solve(Y,n,fres,cres,n);
}
wt(4d9*n-cres);