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# Uses python3
import sys
import queue
def bfs(adj, s, dist):
q = queue.Queue()
q.put(s)
while not q.empty():
u = q.get()
for i in adj[u]:
if dist[i] == -1:
q.put(i)
dist[i] = dist[u] + 1
def distance(adj, s, t):
dist = [-1] * len(adj)
dist[s] = 0
bfs(adj, s, dist)
return dist[t]
if __name__ == '__main__':
input = sys.stdin.read()
data = list(map(int, input.split()))
n, m = data[0:2]
data = data[2:]
edges = list(zip(data[0:(2 * m):2], data[1:(2 * m):2]))
adj = [[] for _ in range(n)]
for (a, b) in edges:
adj[a - 1].append(b - 1)
adj[b - 1].append(a - 1)
s, t = data[2 * m] - 1, data[2 * m + 1] - 1
print(distance(adj, s, t))
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