import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

class Main {

    static class Edege {
        int start, end, weight;

        public Edege(int start, int end, int weight) {
            this.start = start;
            this.end = end;
            this.weight = weight;
        }
    }

    static final int INF = Integer.MAX_VALUE / 2;
    static int n, m, k;
    static int[] dist = new int[510];
    static Edege[] edeges = new Edege[10010];

    static {
        Arrays.fill(dist, INF);
    }

    static boolean generateDistance() {
        dist[1] = 0;
        //循环次数即是走过的边的最大条数
        for (int i = 0; i < k; i++) {
            int[] temp = Arrays.copyOf(dist, n + 1);
            for (int j = 0; j < m; j++) {
                Edege edege = edeges[j];
                //对比当前dist用上次状态的点是否可以更新
                dist[edege.end] = Math.min(dist[edege.end], temp[edege.start] + edege.weight);
                /*if (dist[edege.end] > temp[edege.start] + edege.weight) {
                    dist[edege.end] = temp[edege.start] + edege.weight;
                }*/
            }
        }
        return dist[n] <= INF / 2;
    }

    public static void main(String[] args) throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(isr);
        String[] strs = in.readLine().split(" ");
        n = Integer.parseInt(strs[0]);
        m = Integer.parseInt(strs[1]);
        k = Integer.parseInt(strs[2]);
        for (int i = 0; i < m; i++) {
            strs = in.readLine().split(" ");
            int a = Integer.parseInt(strs[0]);
            int b = Integer.parseInt(strs[1]);
            int w = Integer.parseInt(strs[2]);
            edeges[i] = new Edege(a, b, w);
        }

        if (generateDistance()) System.out.println(dist[n]);
        else System.out.println("impossible");

        in.close();
        isr.close();
    }
}