# n, m = map(int, input().split())
# c = list(map(int, input().split()))

# cnt = [set() for _ in range(n)]
# for i in range(n):
#     cnt[c[i]-1].add(i)

# s = set()
# edge = [0]*n
# for _ in range(m):
#     v, u = map(int, input().split())
#     v -= 1
#     u -= 1
#     if c[v] == c[u]:
#         if (v, u) not in s and (u, v) not in s:
#             edge[c[v]-1] += 1
#             s.add((v, u))
#             s.add((u, v))

# ans = 0
# for e, t in zip(edge, cnt):
#     if len(t) == 0:
#         continue
#     ans += max(len(t)-1-e, 0)
# print(ans)

n, m = map(int, input().split())
g = [[] for _ in range(n)]
for _ in range(m):
    v, u = map(int, input().split())
    v -= 1
    u -= 1
    g[v].append(u)
from collections import deque

def culc_dist(st: int, g: list):
    dist = [-1]*n
    q = deque()
    q.append(st)
    dist[st] = 0
    while q:
        v = q.popleft()
        for nv in g[v]:
            if dist[nv] == -1:
                dist[nv] = dist[v] + 1
                q.append(nv)
    return dist

dist1 = culc_dist(0, g)
dist2 = culc_dist(n-2, g)
dist3 = culc_dist(n-1, g)
if (dist1[n-2] == -1 or dist2[n-1] == -1 or dist3[0] == -1) and (dist3[n-3] == -1 or dist1[n-1] == -1 or dist2[0] == -1):
    print(-1)
elif dist1[n-2] == -1 or dist2[n-1] == -1 or dist3[0] == -1:
    print(dist1[n-1]+dist3[n-2]+dist2[0])
elif dist3[n-3] == -1 or dist1[n-1] == -1 or dist2[0] == -1:
    print(dist1[n-2]+dist2[n-1]+dist3[0])
else:
    print(min(dist1[n-2]+dist2[n-1]+dist3[0], dist1[n-1]+dist3[n-2]+dist2[0]))