# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
from collections import defaultdict as dd
S = input
R = range
P = print
def I(): return int(S())
def M(): return map(int, S().split())
def L(): return list(M())
def O(): return list(map(int, open(0).read().split()))
def yn(b): print("Yes" if b else "No")
biga = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
smaa = "abcdefghijklmnopqrstuvwxyz"
ctoi = lambda c: ord(c) - ord('a')
itoc = lambda i: chr(ord('a') + i)
inf = 10 ** 18
mod = 998244353
def acc(a):
	b = [0]
	for i in a:
		b.append(b[-1] + i)
	return b

from collections import deque

n,m=M()
g=[[] for _ in R(n)]
g2=[[] for _ in R(n)]
for i in R(m):
	u,v=M()
	u-=1;v-=1
	g[u].append(v);g2[v].append(u)

di=[10**18]*n
di[0]=0
q=deque([0])
while q:
	u=q.popleft()
	for v in g[u]:
		if di[v]>di[u]+1:
			di[v]=di[u]+1
			q.append(v)
di2=[10**18]*n
di2[0]=0
q2=deque([0])
while q2:
	u=q2.popleft()
	for v in g2[u]:
		if di2[v]>di2[u]+1:
			di2[v]=di2[u]+1
			q2.append(v)
di3=[10**18]*n
di3[n-1]=0
q3=deque([n-1])
while q3:
	u=q3.popleft()
	for v in g[u]:
		if di3[v]>di3[u]+1:
			di3[v]=di3[u]+1
			q3.append(v)
di4=[10**18]*n
di4[n-1]=0
q4=deque([n-1])
while q4:
	u=q4.popleft()
	for v in g2[u]:
		if di4[v]>di4[u]+1:
			di4[v]=di4[u]+1
			q4.append(v)
ans=min(di[n-1]+di3[n-2]+di2[n-2],di[n-2]+di4[n-2]+di2[n-1])
if ans>10**9:P(-1)
else:P(ans)