from collections import deque


def solve(N, M, G):
    def bfs(start):
        costs = [float("inf")] * N
        costs[start] = 0
        fifo = deque([start])
        while fifo:
            u = fifo.popleft()
            for v in G[u]:
                if costs[v] == float("inf"):
                    costs[v] = costs[u] + 1
                    fifo.append(v)

        return costs

    costs1 = bfs(0)
    costs2 = bfs(N - 2)
    costs3 = bfs(N - 1)

    ans = min(
        costs1[N - 2] + costs2[N - 1] + costs3[0],
        costs1[N - 1] + costs3[N - 2] + costs2[0],
    )
    if ans == float("inf"):
        ans = -1

    return ans


def main():
    N, M = map(int, input().split())
    G = [[] for _ in range(N)]
    for _ in range(M):
        u, v = map(int, input().split())
        u -= 1
        v -= 1
        G[u].append(v)
    ans = solve(N, M, G)
    print(ans)


if __name__ == "__main__":
    main()