Problem: Snuke's town has a subway system, consisting of N stations and M railway lines. The stations are numbered 1 through N. Each line is operated by a company. Each company has an identification number.

The i-th ( 1 \leq i \leq M ) line connects station p_i and q_i bidirectionally. There is no intermediate station. This line is operated by company c_i.

You can change trains at a station where multiple lines are available.

The fare system used in this subway system is a bit strange. When a passenger only uses lines that are operated by the same company, the fare is 1 yen (the currency of Japan). Whenever a passenger changes to a line that is operated by a different company from the current line, the passenger is charged an additional fare of 1 yen. In a case where a passenger who changed from some company A's line to another company's line changes to company A's line again, the additional fare is incurred again.

Snuke is now at station 1 and wants to travel to station N by subway. Find the minimum required fare.

Constraints

* 2 \leq N \leq 10^5
* 0 \leq M \leq 2×10^5
* 1 \leq p_i \leq N (1 \leq i \leq M)
* 1 \leq q_i \leq N (1 \leq i \leq M)
* 1 \leq c_i \leq 10^6 (1 \leq i \leq M)
* p_i \neq q_i (1 \leq i \leq M)

Input

The input is given from Standard Input in the following format:


N M
p_1 q_1 c_1
:
p_M q_M c_M


Output

Print the minimum required fare. If it is impossible to get to station N by subway, print `-1` instead.

Examples

Input

3 3
1 2 1
2 3 1
3 1 2


Output

1


Input

8 11
1 3 1
1 4 2
2 3 1
2 5 1
3 4 3
3 6 3
3 7 3
4 8 4
5 6 1
6 7 5
7 8 5


Output

2


Input

2 0


Output

-1

Solution (in PYTHON3):

Solution:
from collections import defaultdict
from collections import deque

N, M = map(int, input().split())

chg = 10**6
G = defaultdict(set)
for _ in range(M):
    p, q, c = map(int, input().split())
    # 無向グラフ
    G[p].add(p+chg*c)
    G[p+chg*c].add(p)
    G[q].add(q+chg*c)
    G[q+chg*c].add(q)
    G[p+chg*c].add(q+chg*c)
    G[q+chg*c].add(p+chg*c)


dist = defaultdict(lambda: 10**11)
dist[1] = 0

que = deque([1])

while que:
    ci = que.popleft()

    for ni in G[ci]:
        if dist[ni] == 10**11:
            if ci >= chg and ni >= chg:
                dist[ni] = dist[ci]
                que.appendleft(ni)
            else:
                dist[ni] = dist[ci]+1
                que.append(ni)


if dist[N] < 10**11:
    print(dist[N]//2)
else:
    print(-1)