import java.util.*;

public class Main {
    static boolean isArrow;
    static boolean[][] used;
    static long min = Long.MAX_VALUE;
    static ArrayList<HashMap<Integer, Integer>> graph = new ArrayList<>();
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        isArrow = (sc.nextInt() == 1);
        int n = sc.nextInt();
        int m = sc.nextInt();
        for (int i = 0; i < n; i++) {
            graph.add(new HashMap<>());
        }
        for (int i = 0; i < m; i++) {
            int a = sc.nextInt() - 1;
            int b = sc.nextInt() - 1;
            int c = sc.nextInt();
            graph.get(a).put(b, c);
            if (!isArrow) {
                graph.get(b).put(a, c);
            }
        }
        used = new boolean[n][n];
        long[] costs = new long[n];
        for (int i = 0; i < n; i++) {
            Arrays.fill(costs, 0);
            next(i, i, 1, costs);
        }
        if (min == Long.MAX_VALUE) {
            System.out.println(-1);
        } else {
            System.out.println(min);
        }
    }
    
    static void next(int idx, int from, long x, long[] costs) {
        if (costs[idx] != 0) {
            min = Math.min(min, x - costs[idx]);
            return;
        }
        if (used[from][idx]) {
            return;
        }
        used[from][idx] = true;
        costs[idx] = x;
        for (int y : graph.get(idx).keySet()) {
            if (!isArrow && y == from) {
                continue;
            }
            next(y, idx, x + graph.get(idx).get(y), costs);
        }
        costs[idx] = 0;
    }
}