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

def bfs(graph,N,s,t):
    start=time.time()
    S=[s]
    visited=set()
    distance={(i+1,j):0 for i in range(N) for j in range(3)}
    while len(S)>0:
        if time.time()-start==1.7:
            return False,-1
        v=S.pop(0)
        if v==t:
            return True,distance[v]+1
        if v not in visited:
            visited.add(v)
            for w in graph[v]:
                distance[w] = distance[v]+1
                S.append(w)
    return False,-1
if __name__ == '__main__':
    N,M=list(map(int,input().split()))
    E=[list(map(int,input().split())) for _ in range(M)]
    S,T=list(map(int,input().split()))
    graph={(i+1,j):[] for i in range(N) for j in range(3)}
    for e in E:
        graph[(e[0],0)].append((e[1],1))
        graph[(e[0],1)].append((e[1],2))
        graph[(e[0],2)].append((e[1],0))
    flag,ans=bfs(graph,N,(S,0),(T,0))

    if flag:
        print(ans//3)
    else:
        print(-1)

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

def dijkstra(graph,N,s):
    distance = {(i + 1, j): 1e7 for i in range(N) for j in range(3)}
    distance[s]=0
    q=[]
    heapq.heappush(q,(distance[s],s))
    while len(q)>0:
        cost,v=heapq.heappop(q)
        if cost>distance[v]:
            continue
        else:
            for w in graph[v]:
                if distance[w]>distance[v]+1:
                    distance[w]=distance[v]+1
                    heapq.heappush(q,(distance[w],w))
    return distance


if __name__ == '__main__':
    N,M=list(map(int,input().split()))
    E=[list(map(int,input().split())) for _ in range(M)]
    S,T=list(map(int,input().split()))
    graph={(i+1,j):[] for i in range(N) for j in range(3)}
    for e in E:
        graph[(e[0],0)].append((e[1],1))
        graph[(e[0],1)].append((e[1],2))
        graph[(e[0],2)].append((e[1],0))
    distance=dijkstra(graph,N,(S,0))
    d=distance[(T,0)]
    if d%3==0:
        print(d//3)
    else:
        print(-1)

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

def bfs(graph,N,s,t):
    start=time.time()
    S=[s]
    visited=set()
    distance={(i+1,j):0 for i in range(N) for j in range(3)}
    while len(S)>0:
        if time.time()-start==1.9:
            return False,-1
        v=S.pop(0)
        if v==t:
            return True,distance[v]+1
        if v not in visited:
            visited.add(v)
            for w in graph[v]:
                distance[w] = distance[v]+1
                S.append(w)
    return False,-1
if __name__ == '__main__':
    N,M=list(map(int,input().split()))
    E=[list(map(int,input().split())) for _ in range(M)]
    S,T=list(map(int,input().split()))
    graph={(i+1,j):[] for i in range(N) for j in range(3)}
    for e in E:
        graph[(e[0],0)].append((e[1],1))
        graph[(e[0],1)].append((e[1],2))
        graph[(e[0],2)].append((e[1],0))
    flag,ans=bfs(graph,N,(S,0),(T,0))

    if flag:
        print(ans//3)
    else:
        print(-1)

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

def dijkstra(graph,N,s):
    distance = {(i + 1, j): 1e7 for i in range(N) for j in range(3)}
    distance[s]=0
    q=[]
    heapq.heappush(q,(distance[s],s))
    while len(q)>0:
        cost,v=heapq.heappop(q)
        if cost>distance[v]:
            continue
        else:
            for w in graph[v]:
                if distance[w]>distance[v]+1:
                    distance[w]=distance[v]+1
                    heapq.heappush(q,(distance[w],w))
    return distance


if __name__ == '__main__':
    N,M=list(map(int,input().split()))
    E=[list(map(int,input().split())) for _ in range(M)]
    S,T=list(map(int,input().split()))
    graph={(i+1,j):[] for i in range(N) for j in range(3)}
    for e in E:
        graph[(e[0],0)].append((e[1],1))
        graph[(e[0],1)].append((e[1],2))
        graph[(e[0],2)].append((e[1],0))
    distance=dijkstra(graph,N,(S,0))
    d=distance[(T,0)]
    if d%3==0:
        print(d//3)
    else:
        print(-1)

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

def bfs(graph,N,s,t):
    S=[s]
    visited=set()
    distance={(i+1,j):0 for i in range(N) for j in range(3)}
    while len(S)>0:
        v=S.pop(0)
        if v==t:
            return True,distance[v]+1
        if v not in visited:
            visited.add(v)
            for w in graph[v]:
                distance[w] = distance[v]+1
                S.append(w)
    return False,-1
if __name__ == '__main__':
    N,M=list(map(int,input().split()))
    E=[list(map(int,input().split())) for _ in range(M)]
    S,T=list(map(int,input().split()))
    graph={(i+1,j):[] for i in range(N) for j in range(3)}
    for e in E:
        graph[(e[0],0)].append((e[1],1))
        graph[(e[0],1)].append((e[1],2))
        graph[(e[0],2)].append((e[1],0))
    flag,ans=bfs(graph,N,(S,0),(T,0))

    if flag:
        print(ans//3)
    else:
        print(-1)

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

def dijkstra(graph,N,s):
    distance = {(i + 1, j): 1e7 for i in range(N) for j in range(3)}
    distance[s]=0
    q=[]
    heapq.heappush(q,(distance[s],s))
    while len(q)>0:
        cost,v=heapq.heappop(q)
        if cost>distance[v]:
            continue
        else:
            for w in graph[v]:
                if distance[w]>distance[v]+1:
                    distance[w]=distance[v]+1
                    heapq.heappush(q,(distance[w],w))
    return distance


if __name__ == '__main__':
    N,M=list(map(int,input().split()))
    E=[list(map(int,input().split())) for _ in range(M)]
    S,T=list(map(int,input().split()))
    graph={(i+1,j):[] for i in range(N) for j in range(3)}
    for e in E:
        graph[(e[0],0)].append((e[1],1))
        graph[(e[0],1)].append((e[1],2))
        graph[(e[0],2)].append((e[1],0))
    distance=dijkstra(graph,N,(S,0))
    d=distance[(T,0)]
    if d%3==0:
        print(d//3)
    else:
        print(-1)