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 = 'import sys\n\nint1 = lambda x: int(x) - 1\np2D = lambda x: print(*x, sep="\\n")\ndef II(): return int(sys.stdin.readline())\ndef MI(): return map(int, sys.stdin.readline().split())\ndef MI1(): return map(int1, sys.stdin.readline().split())\ndef LI(): return list(map(int, sys.stdin.readline().split()))\ndef LLI(rows_number): return [LI() for _ in range(rows_number)]\ndef SI(): return sys.stdin.readline()[:-1]\n\nfrom collections import deque\n\ndef solve():\n    dist = [inf] * len(to)\n    q = deque()\n    q.append((0, 0))\n    dist[0] = 0\n    while q:\n        d, i = q.popleft()\n        if d > dist[i]: continue\n        if i < n:\n            for j in to[i]:\n                if dist[j] <= d + 1: continue\n                dist[j] = d + 1\n                q.append((d + 1, j))\n        else:\n            for j in to[i]:\n                if j == n - 1:\n                    print(dist[i])\n                    return\n                if dist[j] <= d: continue\n                dist[j] = d\n                q.appendleft((d, j))\n    print(-1)\n\ninf=10**9\nn,m=MI()\nto=[]\nuctoi={}\n\nfor u in range(n):\n    to.append([])\n    uctoi[u,0]=u\n\nfor _ in range(m):\n    u,v,c=MI()\n    u,v=u-1,v-1\n    if (u,c) not in uctoi:\n        i=uctoi[u,c]=len(to)\n        to.append([])\n        to[i].append(u)\n        to[u].append(i)\n    else:i=uctoi[u,c]\n    if (v,c) not in uctoi:\n        j=uctoi[v,c]=len(to)\n        to.append([])\n        to[j].append(v)\n        to[v].append(j)\n    else:j=uctoi[v,c]\n    to[i].append(j)\n    to[j].append(i)\n#print(to)\n#print(fin)\n\nsolve()\n'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

```

Measured memory_bytes: 15847