#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll INF = 1LL << 60;
#define all(a) begin(a), end(a)
#define sz(a) ssize(a)
template<class T, class U> bool chmin(T& a, U b) { return a > b ? a = b, 1 : 0; }
template<class T, class U> bool chmax(T& a, U b) { return a < b ? a = b, 1 : 0; }
using pll = pair<ll, ll>;
using ppll = tuple<ll,ll,ll>;
using vpll = vector<pll>;
using vll = vector<ll>;
using vvll = vector<vll>;
#define _O(_1, _2, _3, n, ...) n
#define _r1(i, n) for(ll i = 0; i < (ll)(n); i++)
#define _r2(i, l, r) for(ll i = (ll)(l); i < (ll)(r); i++)
#define rep(...) _O(__VA_ARGS__, _r2, _r1)(__VA_ARGS__)
#define _rr1(i, n) for(ll i = (ll)(n) - 1; i >= 0; i--)
#define _rr2(i, l, r) for(ll i = (ll)(r) - 1; i >= (ll)(l); i--)
#define rrep(...) _O(__VA_ARGS__, _rr2, _rr1)(__VA_ARGS__)
template<class T, class U> ostream& operator<<(ostream& o, const pair<T,U>& p) {
   return  o << "(" << p.first << "," << p.second << ")";
}
template<class T> ostream& operator<<(ostream& o, const vector<T>& v) {
   ll i = 0;
   for(auto& x : v) o << (i++ ? " " : "") << x;
   return o;
}
template<class H, class... T> void out(const H& h, const T&... t) {
   cout << h;
   ((cout << " " << t), ...);
   cout << endl;
}

int main(){
  ll n,m; cin >> n >> m;
  vector<vector<pll>> g(n);
  rep(i,m){
    ll u, v, c; cin >> u >> v >> c; --u, --v;
    g[u].emplace_back(v,c);
  }
  string s; cin >> s;
  priority_queue<pll,vector<pll>,greater<pll>> q;
  vll dist(n, INF);
  q.emplace(0,0);
  while(!q.empty()){
    auto [d,u] = q.top(); q.pop();
    if(d >= dist[u]) continue;
    dist[u] = d;
    for(auto [v,c] : g[u]) q.emplace(d+c,v);
  }
  rep(i,n) if(s[i] == 'K') q.emplace(dist[i],i);
  fill(all(dist),INF);
  while(!q.empty()){
    auto [d,u] = q.top(); q.pop();
    if(d >= dist[u]) continue;
    dist[u] = d;
    for(auto [v,c] : g[u]) q.emplace(d+c,v);
  }
  priority_queue<ppll,vector<ppll>,greater<ppll>> q2;
  vpll dist1(n,{INF,INF});
  vpll dist2(n,{INF,INF});
  rep(i,n) if(s[i] == 'C') q2.emplace(dist[i],i,i);
  while(!q2.empty()){
    auto [d,u,x] = q2.top(); q2.pop();
    if(d < dist1[u].first) dist1[u] = {d,x};
    else if(d < dist2[u].first && x != dist1[u].second) dist2[u] = {d,x};
    else continue;
    for(auto [v,c] : g[u]) q2.emplace(d+c,v,x);
  }
  rep(i,n) if(s[i] == 'P') {
    q2.emplace(dist1[i].first,i,dist1[i].second);
    q2.emplace(dist2[i].first,i,dist2[i].second);
  }
  fill(all(dist1),pll{INF,INF});
  fill(all(dist2),pll{INF,INF});
  while(!q2.empty()){
    auto [d,u,x] = q2.top(); q2.pop();
    if(d < dist1[u].first) dist1[u] = {d,x};
    else if(d < dist2[u].first && x != dist1[u].second) dist2[u] = {d,x};
    else continue;
    for(auto [v,c] : g[u]) q2.emplace(d+c,v,x);
  }
  ll ans = INF;
  rep(i,n) if(s[i] == 'C') {
    if(dist1[i].second == i) chmin(ans, dist2[i].first);
    else chmin(ans, dist1[i].first);
  }
  out(ans > INF-10 ? -1 : ans );
}