# Uses python3

import sys
import heapq


def distance(adj, cost, s, t):
    if s == t:
        return 0
    dist = [float('inf')] * len(adj)
    visited = [False] * len(adj)
    dist[s] = 0
    q = []
    heapq.heappush(q, (dist[s], s))

    while len(q) != 0:
        u = heapq.heappop(q)[1]
        if visited[u]:
            continue
        visited[u] = True
        if len(adj[u]) > 0:
            for i in range(len(adj[u])):
                if dist[adj[u][i]] > dist[u] + cost[u][i]:
                    dist[adj[u][i]] = dist[u] + cost[u][i]
                    heapq.heappush(q, (dist[adj[u][i]], adj[u][i]))

    if dist[t] == float('inf'):
        return -1
    return dist[t]


if __name__ == '__main__':
    input = sys.stdin.read()
    data = list(map(int, input.split()))
    n, m = data[0:2]
    data = data[2:]
    edges = list(zip(zip(data[0:(3 * m):3], data[1:(3 * m):3]), data[2:(3 * m):3]))
    data = data[3 * m:]
    adj = [[] for _ in range(n)]
    cost = [[] for _ in range(n)]
    for ((a, b), w) in edges:
        adj[a - 1].append(b - 1)
        cost[a - 1].append(w)
    s, t = data[0] - 1, data[1] - 1
    print(distance(adj, cost, s, t))