미래 도시

import sys

input=sys.stdin.readline
INF=int(1e9)

# 전체 회사 개수, 경로의 개수
n, m = map(int, input().split())

graph = [[INF]*(n+1) for _ in range(n+1)]

for i in range(1, n+1):
    graph[i][i]=0

for i in range(m):
    a, b=map(int, input().split())
    graph[a][b]=1
    graph[b][a]=1

# 목적 노드, 거쳐가는 노드
x, k = map(int, input().split())

for _k in range(1, n+1):
    for a in range(1, n+1):
        for b in range(1, n+1):
            graph[a][b] = min(graph[a][b], graph[a][_k]+graph[_k][b])

distance = graph[1][k] + graph[k][x]

if distance >= INF:
    print("-1")
else:
    print(distance)

p. 259