#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<int> cidx;
  rep(i,0,n) if (s[i] == 'C') cidx.eb(i);
  assert(len(cidx) <= 10);
  int l = len(cidx);
  pq<P> que;
  vector<ll> d1(n, inf);
  d1[0] = 0;
  que.emplace(0, 0);
  while(!que.empty()) {
    auto [d, v] = que.top();
    que.pop();
    if (d1[v] < d) continue;
    for (auto [nv, c] : G[v]) {
      if (d1[nv] > d1[v]+c) {
        d1[nv] = d1[v]+c;
        que.emplace(d1[nv], nv);
      }
    }
  }
  vector<vector<ll>> dG(l, vector<ll>(n, inf)), dH(l, vector<ll>(n, inf));
  rep(i,0,l) {
    dG[i][cidx[i]] = 0;
    que.emplace(0, cidx[i]);
    while(!que.empty()) {
      auto [d, v] = que.top();
      que.pop();
      if (dG[i][v] < d) continue;
      for (auto [nv, c] : G[v]) {
        if (dG[i][nv] > dG[i][v]+c) {
          dG[i][nv] = dG[i][v]+c;
          que.emplace(dG[i][nv], nv);
        }
      }
    }
    dH[i][cidx[i]] = 0;
    que.emplace(0, cidx[i]);
    while(!que.empty()) {
      auto [d, v] = que.top();
      que.pop();
      if (dH[i][v] < d) continue;
      for (auto [nv, c] : H[v]) {
        if (dH[i][nv] > dH[i][v]+c) {
          dH[i][nv] = dH[i][v]+c;
          que.emplace(dH[i][nv], nv);
        }
      }
    }
  }
  ll ans = inf;
  rep(i,0,l) rep(j,0,l) if (i != j) {
    ll dKC = inf, dCPC = inf;
    rep(v,0,n) {
      if (s[v] == 'K') chmin(dKC, d1[v]+dH[i][v]);
      if (s[v] == 'P') chmin(dCPC, dG[i][v]+dH[j][v]);
    }
    ans = min(ans, dKC+dCPC);
  }
  if (ans == inf) ans = -1;
  cout << ans << endl;
  return 0;
}