#include <bits/stdc++.h>
#define fi first
#define se second
#define rep(i,s,n) for (int i = (s); i < (n); ++i)
#define rrep(i,g,n) for (int i = (n)-1; i >= (g); --i)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define len(x) (int)(x).size()
#define dup(x,y) (((x)+(y)-1)/(y))
#define pb push_back
#define eb emplace_back
#define Field(T) vector<vector<T>>
using namespace std;
using ll = long long;
using ull = unsigned long long;
template<typename T> using pq = priority_queue<T,vector<T>,greater<T>>;
using P = pair<int,int>;
template<class T>bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T&a,T b){if(b<a){a=b;return 1;}return 0;}

static constexpr ll inf = 100000000000000000;

int main() {
  int n, m;
  cin >> n >> m;
  assert(4 <= n && n <= 200000);
  assert(1 <= m && m <= 300000);
  vector<vector<P>> G(n), H(n);
  set<P> e_set;
  rep(i,0,m) {
    int u, v, c;
    cin >> u >> v >> c;
    assert(1 <= u && u <= n && 1 <= v && v <= n);
    assert(u != v);
    assert(1 <= c && c <= 1000000000);
    e_set.emplace(u, v);
    --u, --v;
    G[u].eb(v, c), H[v].eb(u, c);
  }
  assert(len(e_set) == m);
  string s;
  cin >> s;
  assert(len(s) == n);
  rep(i,0,n) assert('A' <= s[i] && s[i] <= 'Z');
  vector<ll> d1(2*n, inf);
  d1[0] = 0;
  pq<pair<ll,int>> que;
  que.emplace(0, 0);
  while(!que.empty()) {
    auto [cur, v] = que.top();
    que.pop();
    if (d1[v] < cur) continue;
    if (v < n && s[v] == 'K') {
      if (d1[v+n] > d1[v]) {
        d1[v+n] = d1[v];
        que.emplace(d1[v+n], v+n);
      }
    }
    if (v < n) {
      for (auto [nv, c] : G[v]) {
        if (d1[nv] > d1[v]+c) {
          d1[nv] = d1[v]+c;
          que.emplace(d1[nv], nv);
        }
      }
    } else {
      for (auto [nv, c] : G[v-n]) {
        if (d1[nv+n] > d1[v]+c) {
          d1[nv+n] = d1[v]+c;
          que.emplace(d1[nv+n], nv+n);
        }
      }
    }
  }
  function<vector<pair<pair<ll,int>,pair<ll,int>>>(vector<vector<P>> &, vector<pair<int,ll>> &)> f = [](vector<vector<P>> G, vector<pair<int,ll>> &d0) {
    int n = len(G);
    vector<pair<pair<ll,int>,pair<ll,int>>> dist(n, {{inf,-1}, {inf,-1}});
    pq<pair<pair<ll,int>, int>> que;
    for (auto [v, d] : d0) {
      dist[v].fi = {d, v};
      que.emplace(make_pair(d, v), v);
    }
    while(!que.empty()) {
      auto [p, v] = que.top();
      que.pop();
      if (dist[v].fi != p && dist[v].se != p) continue;
      for (auto [nv, c] : G[v]) {
        pair<ll,int> np = {p.fi+c, p.se};
        if (np.fi < dist[nv].fi.fi) {
          if (np.se != dist[nv].fi.se) {
            dist[nv].se = dist[nv].fi;
            dist[nv].fi = np;
          } else {
            dist[nv].fi = np;
          }
          que.push({np, nv});
        } else if (np.fi < dist[nv].se.fi) {
          if (np.se != dist[nv].fi.se) {
            dist[nv].se = np;
            que.push({np, nv});
          }
        }
      }
    }
    return dist;
  };
  vector<pair<int,ll>> dKC0, dC0;
  rep(i,0,n) {
    if (s[i] == 'C') {
      if (d1[i+n] < inf) {
        dKC0.eb(i, d1[i+n]);
      }
      dC0.eb(i, 0);
    }
  }
  auto dKC = f(G, dKC0), dC = f(H, dC0);
  ll ans = inf;
  rep(i,0,n) {
    if (s[i] == 'P') {
      if (dKC[i].fi.se != dC[i].fi.se) ans = min(ans, dKC[i].fi.fi+dC[i].fi.fi);
      if (dKC[i].fi.se != dC[i].se.se) ans = min(ans, dKC[i].fi.fi+dC[i].se.fi);
      if (dKC[i].se.se != dC[i].fi.se) ans = min(ans, dKC[i].se.fi+dC[i].fi.fi);
    }
  }
  if (ans == inf) ans = -1;
  cout << ans << endl;
  return 0;
}