import sys
import io, os
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline

n, m = map(int, input().split())
g = [[] for i in range(n)]
for i in range(m):
    a, b = map(int, input().split())
    a, b = a-1, b-1
    g[a].append(b)
    g[b].append(a)

from collections import deque
q = deque([])
q.append(0)
dist = [-1]*n
dist[0] = 0
while q:
    v = q.popleft()
    for u in g[v]:
        if dist[u] == -1:
            q.append(u)
            dist[u] = dist[v]+1
if dist[n-1] == -1:
    print(-1)
else:
    print(dist[n-1])