задача 1334

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n, m = map(int, input().split())
graph = [[1000000000000 for i in range(n)] for j in range(n)]
for i in range(m):
a, b, c = map(int, input().split())
graph[a-1][b-1] = c
graph[b-1][a-1] = c
for k in range(n):
for i in range(n):
for j in range(n):
if graph[i][k] + graph[k][j] < graph[i][j]:
graph[i][j] = graph[i][k] + graph[k][j]
for i in range(n):
for j in range(n):
if graph[i][j] == 1000000000000:
graph[i][j] = -1
if i == j:
graph[i][i] = 0
print(max([max(i) for i in graph]))
'''
n, m = [int(s) for s in input().split()]
min_dist = [[float('+inf')]*n for i in range(n)]
for i in range(m):
a = [int(s) for s in input().split()]
min_dist[a[0]-1][a[1]-1] = a[2]
min_dist[a[1]-1][a[0]-1] = a[2]
for k in range(n):
for i in range(n):
for j in range(n):
if i == j:
min_dist[i][j] = 0
else:
min_dist[i][j] = min(min_dist[i][j], min_dist[i][k]+min_dist[k][j])
c = 0
for i in range(n):
for elem in min_dist[i]:
if elem > c and elem!=float('+inf'):
c = elem
print(c)
'''