Buggy python submission (verdict: Runtime Error):
from collections import deque

N,M=map(int,input().split())
a=[set() for i in range(N)] # 0-index
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[u].add(v)
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[-1 for i in range(N)]
q0=deque();q1=deque();q2=deque()
q0.append(S);r[S]=0
while q0:
    u=q0.popleft()
    for v in a[u]:
        q1.append(v)
    for w in a[v]:
        q2.append(w)
    for x in a[w]:
        if r[x]==-1:
            r[x]=r[u]+1
            q0.append(x)
# print(r)
print(r[T])

Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

N,M=map(int,input().split())
a=[set() for i in range(N)] # 0-index
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[u].add(v)
S,T=map(lambda x:int(x)-1,input().split())
# print(a)
t=[]
for i in range(N):    
    ti=set()
    for u in a[i]:
        for v in a[u]:
            for w in a[v]:
                ti|={w}    
    t.append(ti)
# print(t)
r=[-1 for i in range(N)]
q=deque()
q.append(S);r[S]=0
while q:
    u=q.popleft()
    for v in t[u]:
        if r[v]==-1:
            r[v]=r[u]+1
            q.append(v)
# print(r)
print(r[T])

Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)

Buggy python submission (verdict: Runtime Error):
from collections import deque

N,M=map(int,input().split())
# 頂点の番号は0-initialのまま扱う
E=set() # 辺から成るset
for i in range(M):
    u,v=map(int,input().split())
    E.add((u,v))
S,T=map(int,input().split())

d1=[set() for i in range(N+1)] # d1[i]=頂点iからの距離が1であるような頂点vから成るset
for e in E:
    u=e[0];v=e[1]
    d1[u].add(v)

d2=[set() for i in range(N+1)] # d2[i]=頂点iからの距離が2であるような頂点vから成るset
for e in E:
    u=e[0];v=e[1]
    d2[u].update(d1[v])

d3=[set() for i in range(N+1)]
for e in E:
    u=e[0];v=e[1]
    d3[u].update(d2[v])
'''
print(e)
print(d1)
print(d2)
print(d3)
'''
#dis=[-1 for i in range(N+1)];dis[S]=0 # 頂点Sからの距離
dis={S:0}
# WFS
q=deque() # 遅ければlistで実装
q.append(S)
while q:
#    print(q) #DB
#    print(dis) #DB
    u=q.popleft()
    #vs=[v for v in d3[u] if dis[v]==-1]
    vs=[v for v in d3[u] if v not in dis]
    for v in vs:
        dis[v]=dis[u]+1
        q.append(v)

print(dis[T])


Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

N,M=map(int,input().split())
# 頂点の番号は0-initialのまま扱う
E=set() # 辺から成るset
for i in range(M):
    u,v=map(int,input().split())
    E.add((u,v))
S,T=map(int,input().split())

d1=[set() for i in range(N+1)] # d1[i]=頂点iからの距離が1であるような頂点vから成るset
for e in E:
    u=e[0];v=e[1]
    d1[u].add(v)

d2=[set() for i in range(N+1)] # d2[i]=頂点iからの距離が2であるような頂点vから成るset
for e in E:
    u=e[0];v=e[1]
    d2[u].update(d1[v])

d3=[set() for i in range(N+1)]
for e in E:
    u=e[0];v=e[1]
    d3[u].update(d2[v])
'''
print(e)
print(d1)
print(d2)
print(d3)
'''
dis=[-1 for i in range(N+1)];dis[S]=0 # 頂点Sからの距離
# WFS
q=deque() # 遅ければlistで実装
q.append(S)
while q:
#    print(q) #DB
#    print(dis) #DB
    u=q.popleft()
    vs=[v for v in d3[u] if dis[v]==-1]
    for v in vs:
        dis[v]=dis[u]+1
    q.extend(vs)

print(dis[T])

Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

N,M=map(int,input().split())
Out=[set() for i in range(N+1)]  # 頂点の番号は0-initialのまま扱う
for i in range(M):
    u,v=map(int,input().split())
    Out[u].add(v)
S,T=map(int,input().split())

Out2=[set() for i in range(N+1)]
for i in range(1,N+1):
    for j in Out[i]:
        Out2[i].update(Out[j])

Out3=[set() for i in range(N+1)]
for i in range(1,N+1):
    for j in Out[i]:
        Out3[i].update(Out2[j])

#print(Out)
#print(Out2)
#print(Out3)

dis=[-1 for i in range(N+1)];dis[S]=0 # 頂点Sからの距離
# WFS
q=deque() # 遅ければlistで実装
q.append(S)
while q:
#    print(q) #DB
#    print(dis) #DB
    u=q.popleft()
    vs=[v for v in Out3[u] if dis[v]==-1]
    for v in vs:
        dis[v]=dis[u]+1
    q.extend(vs)

print(dis[T])


Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

N,M=map(int,input().split())
# 頂点の番号は0-initialのまま扱う
E=set() # 辺から成るset
for i in range(M):
    u,v=map(int,input().split())
    E.add((u,v))
S,T=map(int,input().split())

d1=[set() for i in range(N+1)] # d1[i]=頂点iからの距離が1であるような頂点vから成るset
for e in E:
    u=e[0];v=e[1]
    d1[u].add(v)

d2=[set() for i in range(N+1)] # d2[i]=頂点iからの距離が2であるような頂点vから成るset
for e in E:
    u=e[0];v=e[1]
    d2[u].update(d1[v])

d3=[set() for i in range(N+1)]
for e in E:
    u=e[0];v=e[1]
    d3[u].update(d2[v])
'''
print(e)
print(d1)
print(d2)
print(d3)
'''
dis=[-1 for i in range(N+1)];dis[S]=0 # 頂点Sからの距離
# WFS
q=deque() # 遅ければlistで実装
q.append(S)
while q:
#    print(q) #DB
#    print(dis) #DB
    u=q.popleft()
    vs=[v for v in d3[u] if dis[v]==-1]
    for v in vs:
        dis[v]=dis[u]+1
    q.extend(vs)

print(dis[T])

Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

N,M=map(int,input().split())
Out=[set() for i in range(N+1)]  # 頂点の番号は0-initialのまま扱う
for i in range(M):
    u,v=map(int,input().split())
    Out[u].add(v)
S,T=map(int,input().split())

Out2=[set() for i in range(N+1)]
for i in range(1,N+1):
    for j in Out[i]:
        Out2[i].update(Out[j])

Out3=[set() for i in range(N+1)]
for i in range(1,N+1):
    for j in Out[i]:
        Out3[i].update(Out2[j])

#print(Out)
#print(Out2)
#print(Out3)

dis=[-1 for i in range(N+1)];dis[S]=0 # 頂点Sからの距離
# WFS
q=deque() # 遅ければlistで実装
q.append(S)
while q:
#    print(q) #DB
#    print(dis) #DB
    u=q.popleft()
    vs=[v for v in Out3[u] if dis[v]==-1]
    for v in vs:
        dis[v]=dis[u]+1
    q.extend(vs)

print(dis[T])

Fixed submission:
from collections import deque

N,M=map(int,input().split())
a=[[[] for j in range(N)] for i in range(3)] # 0-indexのグラフが3つある
for i in range(M):
    u,v=map(lambda x:int(x)-1,input().split())
    a[0][u].append((1,v))
    a[1][u].append((2,v))
    a[2][u].append((0,v))
S,T=map(lambda x:int(x)-1,input().split())
# print(a)

r=[[-3 for j in range(N)] for i in range(3)]
q=deque()
q.append((0,S));r[0][S]=0
while q:
    ui,uj=q.popleft()
    for vi,vj in a[ui][uj]:
        if r[vi][vj]==-3:
            r[vi][vj]=r[ui][uj]+1
            q.append((vi,vj))
# print(r)
print(r[0][T]//3)