#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);
  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[v].eb(u, c);
  }
  assert(len(e_set) == m);
  string s;
  cin >> s;
  string t = "KCPC";
  vector<vector<ll>> dp(n, vector<ll>(5, inf));
  dp[0][0] = 0;
  if (s[0] == 'K') dp[0][1] = 0;
  rep(i,0,n) rep(j,0,4) {
    if (s[i] == t[j]) {
      for (auto [pi, c] : G[i]) {
        chmin(dp[i][j+1], dp[pi][j]+c);
      }
    } else {
      for (auto [pi, c] : G[i]) {
        chmin(dp[i][j], dp[pi][j]+c);
      }
    }
  }
  ll ans = inf;
  rep(i,0,n) chmin(ans, dp[i][4]);
  if (ans == inf) ans = -1;
  cout << ans << endl;
  return 0;
}