import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
md = 998244353
# md = 10**9+7

from collections import deque

n, m = LI()
to = [[] for _ in range(n)]
for _ in range(m):
    u, v = LI1()
    to[u].append(v)
    to[v].append(u)

dist = [-1]*n
dist[0] = 0
q = deque()
q.append(0)
while q and dist[n-1] == -1:
    u = q.popleft()
    for v in to[u]:
        if dist[v] == -1:
            dist[v] = dist[u]+1
            q.append(v)

print(dist[n-1])