class Dijkstra():
    class Edge():
        def __init__(self, _to, _cost):
            self.to = _to
            self.cost = _cost

    def __init__(self, V):
        self.G = [[] for i in range(V)]
        self._E = 0
        self._V = V

    @property
    def E(self):
        return self._E

    @property
    def V(self):
        return self._V

    def add(self, _from, _to, _cost):
        self.G[_from].append(self.Edge(_to, _cost))
        self._E += 1

    def shortest_path(self, s):
        import heapq
        que = []
        d = [10**15] * self.V
        d[s] = 0
        heapq.heappush(que, (0, s))

        while len(que) != 0:
            cost, v = heapq.heappop(que)
            if d[v] < cost: continue

            for i in range(len(self.G[v])):
                e = self.G[v][i]
                if d[e.to] > d[v] + e.cost:
                    d[e.to] = d[v] + e.cost
                    heapq.heappush(que, (d[e.to], e.to))
        return d

T = int(input())
N,M = map(int,input().split())
edge = [tuple(map(int,input().split())) for i in range(M)]
res = 10**15

for i in range(M):
    tmp = Dijkstra(N)
    for j in range(M):
        u,v,w = edge[j]
        if i!=j:
            tmp.add(u-1,v-1,w)
            if not T:
                tmp.add(v-1,u-1,w)
    u,v,w = edge[i]
    d = tmp.shortest_path(v-1)[u-1]
    if d!=10**15:
        res = min(res,d+w)

if res!=10**15:
    print(res)
else:
    print(-1)