'''
Bellman-Ford算法，解带负权边的有向图和不带负权边的无向图的单源
最短路问题
'''


class BellmanFord:

    # start_node 为起始点，edges是边的三元组(节点1， 节点2， 边权重) is_directed表示是否是有向图
    def __init__(self, start_node, edges, is_directed, K):
        self.edges = edges[::]
        self.start_node = start_node
        self.is_directed = is_directed
        self.K = K

    # 获取最短路径长度的列表[(节点1，长度1), (节点2, 长度2) .....]
    def getMinPathLen(self):
        return self.getMinInfo(False)

    # 获取所有最短路径列表[(节点1, 长度1, 路径节点列表1)， (节点2, 长度2, 路径节点列表2)]
    def getMinPath(self):
        return self.getMinInfo(True)

    def getMinInfo(self, get_path):
        link = {}
        pre = {}                    # pre[x]表示以节点x结尾的最短路径的前驱节点
        dis, dis_tmp = {}, {}       # 起点到终点的最短距离

        for a, b, w in self.edges:
            if a not in dis:
                dis[a] = 0 if a == self.start_node else 0x7fffffff
            if b not in dis:
                dis[b] = 0 if b == self.start_node else 0x7fffffff

            if not self.is_directed:
                # 无向图检查是否有负边
                if w < 0:
                    return None

                if a not in link:
                    link[a] = []
                if b not in link:
                    link[b] = []

                link[a].append((b, w))
                link[b].append((a, w))

            else:
                if a not in link:
                    link[a] = []
                link[a].append((b, w))

        # 进行V次迭代，第V次检查是否是无解情况
        iter_times = 0
        while iter_times < self.K:
            # 所有边进行松弛操作
            update_flag = False

            for node in dis:
                dis_tmp[node] = dis[node]

            for a in link:
                for b, w in link[a]:
                    new_dis = 0x7fffffff if dis[a] == 0x7fffffff else dis[a] + w
                    if new_dis < dis_tmp[b]:
                        dis_tmp[b] = new_dis
                        pre[b] = a
                        update_flag = True

            dis, dis_tmp = dis_tmp, dis
            iter_times += 1

            if not update_flag:
                break

        # 生成路径函数
        def __getPath(end_node):
            stack = []
            node = end_node
            while True:
                stack.append(node)
                if node not in pre:
                    break
                node = pre[node]
            return stack[::-1]

        return [[node, dis[node], __getPath(node)] for node in dis] if get_path else [[node, dis[node]] for node in dis]

n, m, k = map(int, input().split())
edges = {}
for _ in range(m):
    a, b, w = map(int, input().split())
    if (a, b) not in edges:
        edges[(a, b)] = w
    else:
        edges[(a, b)] = min(edges[(a, b)], w)

edges = [(a, b, w) for (a, b), w in edges.items()]
algo = BellmanFord(1, edges, is_directed=True, K=k)
ans = algo.getMinPathLen()
for k, v in ans:
    if k == n:
        print(v if v != 0x7fffffff else 'impossible')
        break