Buggy python submission (verdict: Runtime Error):
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1
 
que = deque([(0, s)])
already = set()
flg = False
while que:
    cost, cur = que.popleft()
    already.add(cur)
    if cur == t:
        flg = True
        break
    for i in graph[cur]:
        if i not in already:
            que.append((cost + 1, i))
if not flg:
    cost = -1
else:
    cost //= 3
print(cost)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [(0, s)]
flg = False
parent = [-1 for i in range(3 * n)]
while que:
    cost, cur = que[0]
    que.pop(0)
    if cur == t:
        flg = True
        break
    for i in graph[cur]:
        if parent[cur] != i:
            que.append((cost + 1, i))
            parent[i] = cur
if not flg:
    cost = -1
else:
    cost //= 3

print(cost)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = deque([(0, s)])
already = set()
flg = False
while que:
    cost, cur = que.popleft()
    already.add(cur)
    if cur == t:
        flg = True
        break
    for i in graph[cur]:
        if i not in already:
            que.append((cost + 1, i))
if not flg:
    cost = -1
else:
    cost //= 3

print(cost)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import heapq
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [(0,s)]
already = set()
flg = False
while que:
    cost, cur = heapq.heappop(que)
    already.add(cur)
    if cur == t:
        flg = True
        break
    for i in graph[cur]:
        if i in already:
            continue
        heapq.heappush(que, (cost + 1, i))
if not flg:
    cost = -1
else:
    cost //= 3

print(cost)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import heapq
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = [[0 for i in range(3 * n)] for j in range(3 * n)]
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u][n+v] = 1
    graph[u+n][2*n+v] = 1
    graph[u + 2 * n][v] = 1
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [(0,s)]
already = set()
flg = False
while que:
    cost, cur = heapq.heappop(que)
    already.add(cur)
    if cur == t:
        flg = True
        break
    for i, _next in enumerate(graph[cur]):
        if _next == 0:
            continue
        if i in already:
            continue
        heapq.heappush(que, (cost + 1, i))
if not flg:
    cost = -1
else:
    cost //= 3

print(cost)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import heapq
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = [[0 for i in range(3 * n)] for j in range(3 * n)]
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u][n+v] = 1
    graph[u+n][2*n+v] = 1
    graph[u + 2 * n][v] = 1
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

def dijkstra(graph, s, g):
    que = [(0,s)]
    already = set()
    flg = False
    while que:
        cost, cur = heapq.heappop(que)
        already.add(cur)
        if cur == g:
            flg = True
            break
        for i, _next in enumerate(graph[cur]):
            if _next == 0:
                continue
            if i in already:
                continue
            heapq.heappush(que, (cost + 1, i))
    if not flg:
        cost = -1
        return cost
    return cost // 3

res = dijkstra(graph, s, t)
print(res)

Fixed submission:
import sys
INF = 10 ** 9
n, m = [int(i) for i in sys.stdin.readline().split()]
graph = {j:[] for j in range(3 * n)}
for i in range(m):
    u, v = [int(i) for i in sys.stdin.readline().split()]
    u -= 1
    v -= 1
    graph[u].append(n+v)
    graph[u+n].append(2*n+v)
    graph[u + 2 * n].append(v)
s, t = [int(i) for i in sys.stdin.readline().split()]
s -= 1
t -= 1

que = [s]
flg = False
already = set()
dist = [INF for i in range(3 * n)]
dist[s] = 0
while que:
    cur= que[0]
    que.pop(0)
    for i in graph[cur]:
        if i not in already:
            if i == t:
                res = dist[cur] + 1
                que.clear()
                flg = True
                break
            que.append(i)
            dist[i] = dist[cur] + 1
            already.add(i)
if not flg:
    res = -1
else:
    res //= 3

print(res)