from collections import deque

def bfs(graph, n):

    q = deque()

    q.append([1, 0])

    dist = [float('inf') for i in range(n+1)]

    dist[1] = 0

​

    # BFS

    while q:

        x,wt=q.popleft() # 

        for child in graph[x]:

            node,dis= child

            if wt+dis < dist[node]:

                if dis == 0:

                    q.appendleft([node, wt])

                    dist[node] = wt

                else:

                    q.append([node, wt+1])

                    dist[node] = wt+1

​

    print((dist[n] if dist[n] != float('inf') else -1))

​

​

​

n, m = map(int, input().split(' '))

graph = {}

visited = {}

for i in range(1, n+1):

    graph[i] = []

    visited[i] = []

​

​

for i in range(m):

    u,v = map(int, input().strip().split(' '))

    graph[u].append([v,0])

    graph[v].append([u,1])

​

​

bfs(graph, n)

​

​