from heapq import heappush, heappop INF = 1 << 60 # ダイクストラ法 def dijkstra(start, G): costs = [INF]*len(G) costs[start] = 0 pq = [] heappush(pq, (0, start)) while pq: now_t, now_v = heappop(pq) if costs[now_v] < now_t: continue for next_t, next_v in G[now_v]: if costs[next_v] > costs[now_v] + next_t: costs[next_v] = costs[now_v] + next_t heappush(pq, (now_t + next_t, next_v)) return costs N, M = map(int, input().split()) graph = [[] for _ in range(N)] graph_rev = [[] for _ in range(N)] for _ in range(M): u, v, t = map(int, input().split()) u -= 1; v -= 1 graph[u].append((t, v)) graph_rev[v].append((t, u)) di = { N-2: dijkstra(N-2, graph), N-1: dijkstra(N-1, graph) } di_rev = { N-2: dijkstra(N-2, graph_rev), N-1: dijkstra(N-1, graph_rev) } for i in range(N-2): ans_1 = di_rev[N-2][i] + di[N-2][N-1] + di[N-1][i] ans_2 = di_rev[N-1][i] + di[N-1][N-2] + di[N-2][i] ans = min(ans_1, ans_2) if ans < INF: print(ans) else: print(-1)