Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[v-1].append(u-1)
T,St = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
hoge = [0]*N
i = 0
while queue != []:
    i += 1
    l = 0
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge[:l]:
                    hoge[l] = s
                    l += 1
    queue = hoge[:l]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Fixed submission:
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
i = 0
while queue != []:
    i += 1
    hoge = []
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge:
                    hoge.append(s)
    queue = hoge[:]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
hoge = [0]*N
i = 0
while queue != []:
    i += 1
    l = 0
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge[:l]:
                    hoge[l] = s
                    l += 1
    queue = hoge[:l]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Fixed submission:
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
i = 0
while queue != []:
    i += 1
    hoge = []
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge:
                    hoge.append(s)
    queue = hoge[:]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
hoge = [0]*N
for i in range(1,N*3+3):
    l = 0
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge[:l]:
                    hoge[l] = s
                    l += 1
    queue = hoge[:l]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Fixed submission:
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
i = 0
while queue != []:
    i += 1
    hoge = []
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge:
                    hoge.append(s)
    queue = hoge[:]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
hoge = [0]*N
for i in range(1,N*3+3):
    l = 0
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge[:l]:
                    hoge[l] = s
                    l += 1
    queue = hoge[:l]
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Fixed submission:
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
i = 0
while queue != []:
    i += 1
    hoge = []
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge:
                    hoge.append(s)
    queue = hoge[:]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S1 = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S1[u-1].append(v-1)
St,T = map(int,input().split())
S = [[]for i in range(N)]
for i in range(N):
    for k in S1[i]:
        for ken in S1[k]:
            for pa in S1[ken]:
                S[i].append(pa)
D = [float('inf')]*N
D[St-1] = 0
queue = [St-1]
hoge = [0]*N
while queue != []:
    l =0
    for q in queue:
        for i in S[q]:
            if D[i] > D[q]:
                D[i] = D[q]+1
                if not i in hoge[:l]:
                    hoge[l] = i
                    l += 1
    queue = hoge[:l]
if D[T-1] == float('inf'):
    print(-1)
else:
    print(D[T-1])

Fixed submission:
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
i = 0
while queue != []:
    i += 1
    hoge = []
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge:
                    hoge.append(s)
    queue = hoge[:]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
hoge = [0]*N
for i in range(1,N*3+3):
    l = 0
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > D[q][(i-1)%3]:
                D[s][i%3] = D[q][(i-1)%3]+1
                if not s in hoge[:l]:
                    hoge[l] = s
                    l += 1
    queue = hoge[:l]
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)

Fixed submission:
import sys
input = sys.stdin.readline

N,M = map(int,input().split())
S = [[]for i in range(N)]
for i in range(M):
    u,v = map(int,input().split())
    S[u-1].append(v-1)
St,T = map(int,input().split())

D = [[float('inf')]*3 for i in range(N)]
D[St-1][0] = 0
queue = [St-1]
i = 0
while queue != []:
    i += 1
    hoge = []
    for q in queue:
        for s in S[q]:
            if D[s][i%3] > i:
                D[s][i%3] = i
                if not s in hoge:
                    hoge.append(s)
    queue = hoge[:]
    if D[T-1][0] != float('inf'):
        break
if D[T-1][0] == float('inf'):
    print(-1)
else:
    print(D[T-1][0]//3)