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

template<int k>
struct Topk{
	using S=long long;
	S inf=1e18;
	array<S,k> a;
	array<int,k> id;
	Topk(){
		for (int i=0;i<k;i++){
			a[i]=-inf;
			id[i]=-1-i;
		}
	}

	void update(int i){
		while (i>0&&a[i-1]<a[i]){
			swap(a[i-1],a[i]);
			swap(id[i-1],id[i]);
			i--;
		}
	}
	bool add(S x,int y){
		for (int i=0;i<k;i++){
			if (id[i]==y){
				if (a[i]<x){
					a[i]=x;
					update(i);
          return true;
				}
				else return false;
			}
		}
		if (a[k-1]<x){
			a[k-1]=x;
			id[k-1]=y;
			update(k-1);
      return true;
		}
    return false;
	}
	Topk merge(Topk r){
		Topk ret=(*this);
		for (int i=0;i<k;i++) ret.add(r.a[i],r.id[i]);
		return ret;
	}
	S sum(int id,int c){
		S ret=0;
		int cnt=0;
		for (int i=0;i<k;i++){
			if (cnt<c&&(*this).id[i]>=0&&(*this).id[i]!=id){
				ret+=(*this).a[i];
				cnt++;
			}
		}
		if (cnt<c) return -inf;
		return ret;
	}
};

using top2=Topk<2>;

int main(){
  using ll=long long;
  ll inf=1e18;
  int n,m;
  cin>>n>>m;
  vector<vector<pair<int,ll>>> g(n);
  for (int i=0;i<m;i++){
    int u,v,c;
    cin>>u>>v>>c;
    u--;v--;
    g[u].push_back({v,c});
  }
  string s;
  cin>>s;
  vector dist(n,vector<top2>(5));
  priority_queue<tuple<ll,int,int,int>> q;
  q.push({0,0,0,n});
  string t="KCPC#";
  while (!q.empty()){
    auto [d,v,k,u]=q.top();
    q.pop();
    if (!dist[v][k].add(d,u)) continue;
    if (t[k]==s[v]&&u!=v){
      int nu=u;
      if (k==1) nu=v;
      q.push({d,v,k+1,u});
    }
    for (auto [w,c]:g[v]){
      q.push({d-c,w,k,u});
    }
  }
  ll ans=inf;
  for (int v=0;v<n;v++){
    ans=min(ans,-dist[v][4].a[0]);
  }
  if (ans==inf) cout<<-1<<endl;
  else cout<<ans<<endl;
}