变量名都设置成 i, x, t, q, n 这种的可读性真的很差
coding style 负分

from collections import deque
def bfs(graph, d, n):
    # 起点是1
    queue = deque([1])
    d[1] = 0
    # bfs
    while queue:
        cur = queue.popleft()
        # 确保cur有nxt
        if cur in graph:
            # 遍历所有的下一个next点
            for nxt in graph[cur]:
                if d[nxt] == -1:
                    d[nxt] = d[cur] + 1
                    queue.append(nxt)
    # 目标点是n
    print(d[n])

def main():
    n, m = map(int, input().split())
    # 图存储模板
    graph = {}
    for _ in range(m):
        a, b = map(int, input().split())
        if a not in graph:
            graph[a] = [b]
        else:
            graph[a].append(b)

    # d: distance   d[1] - d[4]  4个点
    d = [-1] * (n + 1)
    bfs(graph, d, n)

main()