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

vector<long long> dijkstra(vector<vector<pair<int,long long>>> &Graph,int start){
int N = Graph.size();
//O((V+E)logV) 一般最短経路魔法.
long long inf = 3e18;
    vector<bool> used(N);
    vector<long long> ret(N,inf);
    priority_queue<pair<long long,int>,vector<pair<long long,int>>,greater<pair<long long,int>>> Q;
    ret.at(start) = 0; Q.push({0,start});
    while(Q.size()){
        auto[nowd,pos] = Q.top(); Q.pop();
        if(used.at(pos)) continue;
        used.at(pos) = true;
        for(auto [to,w] : Graph.at(pos)){
            if(ret.at(to) > nowd+w){
                ret.at(to) = nowd+w;
                Q.push({ret.at(to),to});
            }
        }
    }
    return ret;
}
vector<long long> dijkstra2(vector<vector<pair<int,long long>>> &Graph,int start){
    int N = Graph.size();
    //O(V^2) 密グラフ専用.
    long long inf = 3e18;
    vector<bool> used(N);
    vector<long long> ret(N,inf);
    ret.at(start) = 0;
    while(true){
        long long nowd = inf,pos = -1;
        for(int i=0; i<N; i++){
            if(used.at(i)) continue;
            if(nowd > ret.at(i)) nowd = ret.at(i),pos = i;
        }
        if(pos == -1) break;
        used.at(pos) = true;
 
        for(auto [to,w] : Graph.at(pos)){if(ret.at(to) > nowd+w) ret.at(to) = nowd+w;}
    }
    return ret;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int N,M; cin >> N >> M;
    vector<vector<pair<int,long long>>> Graph(N+1);
    for(int i=0; i<M; i++){
        int u,v; cin >> u >> v;
        u--; v--;
        int w; cin >> w;
        Graph.at(u).push_back({v,w});
    }
    string s; cin >> s;
    auto D = dijkstra(Graph,0);
    for(int i=0; i<N; i++) if(s.at(i) == 'K') Graph.at(N).push_back({i,D.at(i)});
    D = dijkstra(Graph,N);

    vector<tuple<long long,int,long long,int>> dist(N,{1e18,-1,1e18,-1});
    priority_queue<tuple<long long,int,int>,vector<tuple<long long,int,int>>,greater<>> Q;
    auto update = [&](int pos,long long d,int c) -> void {
        auto &[d1,c1,d2,c2] = dist.at(pos);
        if(c == c1){
            if(d < d1) d1 = d,Q.push({d,pos,c});
            return;
        }
        if(c == c2){
            if(d < d2){
                d2 = d,Q.push({d,pos,c});
                if(d1 > d2) swap(d2,d1),swap(c2,c1);
            }
            return;
        }
        if(d < d1) d2 = d1,c2 = c1,d1 = d,c1 = c,Q.push({d,pos,c});
        else if(d < d2) d2 = d,c2 = c,Q.push({d,pos,c});
    };
    for(int i=0; i<N; i++) if(s.at(i) == 'C') update(i,D.at(i),i);

    while(Q.size()){
        auto [nowd,pos,c] = Q.top(); Q.pop();
        auto [d1,c1,d2,c2] = dist.at(pos);
        if(!((d1 == nowd && c1 == c) || (d2 == nowd && c2 == c))) continue;
        for(auto [to,w] : Graph.at(pos)) update(to,nowd+w,c);
    }

    vector<tuple<long long,int,long long,int>> dist2(N,{1e18,-1,1e18,-1});
    swap(dist,dist2);
    for(int i=0; i<N; i++) if(s.at(i) == 'P'){
        auto [d1,c1,d2,c2] = dist2.at(i);
        update(i,d1,c1),update(i,d2,c2);
    }
    while(Q.size()){
        auto [nowd,pos,c] = Q.top(); Q.pop();
        auto [d1,c1,d2,c2] = dist.at(pos);
        if(!((d1 == nowd && c1 == c) || (d2 == nowd && c2 == c))) continue;
        for(auto [to,w] : Graph.at(pos)) update(to,nowd+w,c);
    }
    long long answer = 1e18;
    for(int i=0; i<N; i++) if(s.at(i) == 'C'){
        auto [d1,c1,d2,c2] = dist.at(i);
        if(c1 != -1 && c1 != i) answer = min(answer,d1);
        if(c2 != -1 && c2 != i) answer = min(answer,d2);
    }
    if(answer > 1e17) answer = -1;
    cout << answer << endl;
}