from collections import deque

n = int(input())
a, b = map(int, input().split())
m = int(input())

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

for i in range(m):
    x, y = map(int, input().split())
    graph[x].append(y)
    graph[y].append(x)

vis = [0] * (n + 1)

dq = deque([a])
vis[a] = 1

while dq:
    cur = dq.popleft()

    for next in graph[cur]:
        if vis[next] == 0:
            vis[next] = vis[cur] + 1
            dq.append(next)

print(vis[b] - 1)