from kata_207 import dijkstra

def network_delay(n, edges, start):
    adj = [[] for _ in range(n)]
    for u, v, delay in edges:
        adj[u - 1].append((v - 1, delay))
    distances = dijkstra(adj, start - 1)
    return -1 if any(value is None for value in distances) else max(distances)