#############################################################

import sys
sys.setrecursionlimit(10**7)

from heapq import heappop,heappush
from collections import deque,defaultdict,Counter
from bisect import bisect_left, bisect_right
from itertools import product,combinations,permutations
from math import sin,cos
#from math import isqrt #DO NOT USE PyPy

ipt = sys.stdin.readline
iin = lambda :int(ipt())
lmin = lambda :list(map(int,ipt().split()))

INF = 1<<30

def bfs01(s,N,G):
    dq = deque()
    dq.append(s)
    cost = [INF]*N
    cost[s] = 0
    while dq:
        cur = dq.pop()
        for nxt in G[cur]:
            if cost[nxt] != INF:
                continue
            cost[nxt] = cost[cur]+1
            dq.appendleft(nxt)
    return cost
#############################################################

N,M = lmin()
G = [[] for _ in range(N)]
for _ in range(M):
    a,b = lmin()
    G[a-1].append(b-1)

cost1 = bfs01(0,N,G)
cost2 = bfs01(N-2,N,G)
cost3 = bfs01(N-1,N,G)

ans = min(cost1[N-2]+cost2[N-1]+cost3[0],cost1[N-1]+cost3[N-2]+cost2[0])
if ans >= INF:
    print(-1)
else:
    print(ans)