import sys
readline = sys.stdin.readline
from collections import deque


def bfs(G, s, N):
    Q = deque([])
    dist = [-1] * N
    par = [-1] * N
    dist[s] = 0
    for u in G[s]:
        par[u] = s
        dist[u] = 1
        Q.append(u)

    while Q:
        u = Q.popleft()
        for v in G[u]:
            if dist[v] != -1:
                continue
            dist[v] = dist[u] + 1
            par[v] = u
            Q.append(v)
            
    return dist


N, M = map(int, readline().split())
G = [[] for i in range(N)]
for i in range(M):
    a, b = map(int, readline().split())
    a, b = a - 1, b - 1
    G[a].append(b)
    G[b].append(a)
    
D = bfs(G, 0, N)
print(D[-1])