from collections import deque
from heapq import heappop
from math import inf, isinf


def bfs_dist(graph: list[set[int]], start: int, goal: int) -> int | float:
    distance = [inf for _ in graph]
    distance[start] = 0
    queue = deque([start])
    visited = set()
    while queue:
        current = queue.popleft()
        visited.add(current)
        for dest in graph[current]:
            if dest in visited:
                continue
            queue.append(dest)
            distance[dest] = distance[current] + 1

    return distance[goal]


def main():
    N, M = map(int, input().split())
    graph = [set() for _ in range(N)]
    for _ in range(M):
        a, b = map(int, input().split())
        graph[a - 1].add(b - 1)
        graph[b - 1].add(a - 1)

    if isinf((dist := bfs_dist(graph, 0, N - 1))):
        print(-1)
    else:
        print(dist)


if __name__ == "__main__":
    main()