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.

-----Sample Input-----
3 3
1 2 1
2 3 1
3 1 2

-----Sample Output-----
1

Use company 1's lines: 1 → 2 → 3. The fare is 1 yen.

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

ns = {"__name__": "__main__"}
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = '# coding: utf-8\n# Your code here!\nimport sys\nreadline = sys.stdin.readline\nread = sys.stdin.read\n\nn,m = list(map(int, readline().split()))\n\ng = {}\n\nfor _ in range(m):\n    p,q,c = list(map(int, readline().split()))\n    pc = ((p-1)<<20)+c\n    qc = ((q-1)<<20)+c\n    pp = (p-1)<<20\n    qq = (q-1)<<20\n    \n    if pc not in g: g[pc] = []\n    if qc not in g: g[qc] = []\n    if pp not in g: g[pp] = []\n    if qq not in g: g[qq] = []\n    \n    g[pc].append(qc)\n    g[pc].append(pp)\n\n    g[qc].append(pc)\n    g[qc].append(qq)\n\n    g[pp].append(pc)\n    g[qq].append(qc)\n\nif 0 not in g: g[0] = []\n\nfrom collections import deque\nq = deque([(0,0)])\nres = {0:0}\n\nmask = (1<<20)-1\nwhile q:\n    vl,dv = q.popleft()\n    if res[vl] < dv: continue\n    if (vl>>20) == n-1:\n        res[(n-1)<<20] = dv+1\n        break\n    for tl in g[vl]:\n        ndv = dv + (vl&mask==0 or tl&mask==0)\n        if tl not in res or res[tl] > ndv:\n            res[tl] = ndv\n            if vl&mask==0 or tl&mask==0:\n                q.append((tl,ndv))\n            else:\n                q.appendleft((tl,ndv))\n\nif (n-1)<<20 in res:\n    print((res[(n-1)<<20]//2))\nelse:\n    print((-1))\n\n\n\n\n'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

```

Measured memory_bytes: 14183