#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
#define rep(i, n) REP(i, 0, n)
#define REP(i, s, e) for (int i = (s); i < (int)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for (int i = (int)(s - 1); i >= (int)(e); i--)
#define all(r) r.begin(), r.end()
#define rall(r) r.rbegin(), r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

template <typename T, typename U>
T chmax(T& a, const U& b) {
    if (a >= b) return false;
    a = b;
    return true;
}
template <typename T, typename U>
T chmin(T& a, const U& b) {
    if (a <= b) return false;
    a = b;
    return true;
}

void yes_no(bool f, string yes = "Yes", string no = "No") { cout << (f ? yes : no) << "\n"; }

void solve() {
    int n, m;
    cin >> n >> m;
    using P = pair<ll, ll>;
    vector<vector<P>> es(n);
    rep(i, m) {
        int a, b, c;
        cin >> a >> b >> c;
        --a;
        --b;
        es[a].emplace_back(b, c);
    }
    string s;
    cin >> s;
    const int ma = 5;
    const ll inf = 1e18;
    vector d(n, vl(ma, inf));
    d[0][0] = 0;
    using T = tuple<ll, ll, ll>;
    priority_queue<T, vector<T>, greater<T>> q;
    q.emplace(0, 0, 0);
    if (s[0] == 'K') {
        d[0][1] = 0;
        q.emplace(0, 0, 1);
    }
    while (q.size()) {
        auto [v, cur, dig] = q.top();
        q.pop();
        if (d[cur][dig] != v) continue;
        for (auto&& [nxt, cost] : es[cur]) {
            int ndig = dig;
            if ((dig == 0 && s[nxt] == 'K') || ((dig == 1 || dig == 3) && s[nxt] == 'C') || (dig == 2 && s[nxt] == 'P')) {
                ndig++;
            }
            ll ncost = cost + v;
            assert(ndig < ma);
            if (d[nxt][ndig] > ncost) {
                d[nxt][ndig] = ncost;
                q.emplace(ncost, nxt, ndig);
            }
        }
    }
    ll ans = inf;
    rep(i, n) chmin(ans, d[i][ma - 1]);
    if (ans == inf) {
        ans = -1;
    }
    cout << ans << "\n";
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t = 1;
    // cin >> t;
    rep(ti, t) solve();
    return 0;
}