#include <bits/stdc++.h>
using namespace std;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int s, p, t;
    cin >> s >> p >> t;
    vector<int> pp(s + 1);
    vector th(s + 1, vector<int>(26, -1));
    for (int i = 0, u; i < p; i += 1) {
        cin >> u;
        pp[u] = 1;
    }
    vector<vector<pair<int, char>>> G(s + 1);
    for (int i = 0, u, v; i < t; i += 1) {
        char c;
        cin >> u >> c >> v;
        G[u].emplace_back(v, c);
        if (isupper(c)) th[u][c - 'A'] = v;
    }
    int ans = -1;
    vector fd(s + 1, vector<int>(s + 1, -1));
    vector sd(s + 1, -1);
    for (int i = 1; i <= s; i += 1) {
        queue<int> q;
        for (auto [v, w] : G[i])
            if (islower(w) and fd[i][v] == -1) {
                fd[i][v] = 1;
                q.push(v);
            }
        while (not q.empty()) {
            int u = q.front();
            q.pop();
            for (auto [v, w] : G[u])
                if (islower(w) and fd[i][v] == -1) {
                    fd[i][v] = fd[i][u] + 1;
                    q.push(v);
                }
        }
    }
    {
        sd[1] = 0;
        queue<int> q;
        q.push(1);
        while (not q.empty()) {
            int u = q.front();
            q.pop();
            for (auto [v, w] : G[u])
                if (sd[v] == -1) {
                    sd[v] = sd[u] + 1;
                    q.push(v);
                }
        }
    }
    auto update = [&](int& x, int y) {
        if (x == -1 or y < x) {
            x = y;
            return true;
        }
        return false;
    };
    for (int i = 1; i <= s; i += 1)
        if (pp[i])
            for (int j = 1; j <= s; j += 1)
                if (pp[j])
                    if (sd[i] != -1 and fd[i][j] != -1)
                        update(ans, sd[i] * 2 + fd[i][j]);
    vector d(s + 1, vector<int>(s + 1, -1));
    queue<pair<int, int>> q;
    for (int i = 1; i <= s; i += 1)
        if (sd[i] != -1) {
            for (auto [v1, w1] : G[i])
                for (auto [v2, w2] : G[i])
                    if (w1 != w2 and islower(w1) and islower(w2)) {
                        if (update(d[v1][v2], sd[i] * 2 + 2))
                            q.emplace(v1, v2);
                    }
        }
    while (not q.empty()) {
        auto [u1, u2] = q.front();
        //cout << u1 << " " << u2 << " " << d[u1][u2] << endl;
        q.pop();
        if (pp[u1] and pp[u2]) {
            update(ans, d[u1][u2]);
        }
        for (auto [v1, w1] : G[u1])
            if (islower(w1) and update(d[v1][u2], d[u1][u2] + 1))
                q.emplace(v1, u2);
        for (auto [v2, w2] : G[u1])
            if (islower(w2) and update(d[u1][v2], d[u1][u2] + 1))
                q.emplace(u1, v2);
        for (int i = 0; i < 26; i += 1)
            if (th[u1][i] != -1 and th[u2][i] != -1
                and update(d[th[u1][i]][th[u2][i]], d[u1][u2] + 2))
                q.emplace(th[u1][i], th[u2][i]);
    }
    cout << ans;
    return 0;
}