import sys
from collections import deque,defaultdict
import itertools
import heapq
import bisect
import math

#sys.setrecursionlimit(10 ** 9)
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
ml = lambda: map(str, input().split())
li = lambda: list(mi())
li_st = lambda: list(map(str, input().split()))
lli = lambda n: [li() for _ in range(n)]
mod = 998244353
INF = 10**18

N,M = mi()
G = [[] for _ in range(N)]

for i in range(M):
    u,v = mi()
    u -= 1
    v -= 1
    G[u].append(v)

check = [INF] * N
check2 = [INF] * N
check3 = [INF] * N
q = deque()
q.append((0,0,-1))
check[0] = 0

while(q):
    now,times,flag = q.popleft()
    for nxt in G[now]:
        if check[nxt] == INF:
            q.append((nxt,times+1,flag))
            check[nxt] = min(times + 1, check[nxt])
        else:
            check[nxt] = min(times+1,check[nxt])

if check[N-2] != INF:
    q = deque()
    q.append((N-2,0))
    check2[N-2] =  0
    while(q):
        now,times = q.popleft()          
        for nxt in G[now]:
            if check2[nxt] == INF:
                q.append((nxt,times+1))
                check2[nxt] = min(check2[nxt],times + 1)
            else:
                check2[nxt] = min(check2[nxt],times+1)
        if now == 0:
            break

if check[N-1] != INF:
    q = deque()
    q.append((N-1,0))
    check3[N-1] =  0
    while(q):
        now,times = q.popleft()
        for nxt in G[now]:
            if check3[nxt] == INF:
                q.append((nxt,times+1))
                check3[nxt] = min(check3[nxt],times + 1)
            else:
                check3[nxt] = min(check3[nxt],times+1)
        if now == 0:
            break

ans1 = check[N-1] + check3[N-2] + check2[0]
ans2 = check[N-2] + check2[N-1] + check3[0]

#print(check)
#print(check2)
#print(check3)
#print(ans1,ans2)
print(min(ans1,ans2) if min(ans1,ans2) < INF else -1)