Buggy python submission (verdict: Runtime Error):
use = int(input())

if use < 4:
    print(1)
elif use < 8:
    print(4)
elif use < 16:
    print(8)
elif use < 32:
    print(16)
elif use < 64:
    print(32)
elif use > 63:
    print(64)

Fixed submission:
d = {}

def bfs(graph, start, goal): 
#These variables define the visited set (to make sure that the program doesn’t go through the same nodes twice) a queue to make sure that the node seen next is visted first. 
 
    visited, queue = set(), [start] 
    pathsTo = {} 
    pathsTo[start] = [start] 
    index = 0
    lenqueue = 1
# Ensuring that the queue is not empty at any point in time. 
    while index < lenqueue: 
# Getting the next node and getting rid of the node in the front of the queue. 
        vertex = queue[index] 
        if vertex not in visited: 
            visited.add(vertex) 
 
 
            # Going through each element in the adjacency list and making sure that it hasn’t been visited, and that it is not in the same path. 
            for newVertex in (graph[vertex]): 
                if newVertex not in visited: 
                    if newVertex not in pathsTo: 
                        pathsTo[newVertex] = list() 
 
                    for path in pathsTo[vertex]: 
                        pathsTo[newVertex].append(str(path)+"->"+str(newVertex)) 
                    queue.append(newVertex)
                    lenqueue += 1
        index += 1
    # Return the paths toward the goal.
    if goal not in pathsTo.keys():
        return ["8384793->8->4->7-> 9 8 23748"]
    return pathsTo[goal] 

N, M = map(int,input().split())
for i in range(M):
    a,b = map(int,input().split())
    if a not in d.keys():
        d[a] = [b]
    else:
        d[a].append(b)

    if b not in d.keys():
        d[b] = [a]
    else:
        d[b].append(a)

dist = len(bfs(d,1,N)[0].split("->")) - 1
if dist <= 2:
    print("POSSIBLE")
else:
    print("IMPOSSIBLE")

Buggy python submission (verdict: Runtime Error):
use = int(input())

if use < 4:
    print(1)
elif use < 8:
    print(4)
elif use < 16:
    print(8)
elif use < 32:
    print(16)
elif use < 64:
    print(32)
else:
    print(64)
        

Fixed submission:
d = {}

def bfs(graph, start, goal): 
#These variables define the visited set (to make sure that the program doesn’t go through the same nodes twice) a queue to make sure that the node seen next is visted first. 
 
    visited, queue = set(), [start] 
    pathsTo = {} 
    pathsTo[start] = [start] 
    index = 0
    lenqueue = 1
# Ensuring that the queue is not empty at any point in time. 
    while index < lenqueue: 
# Getting the next node and getting rid of the node in the front of the queue. 
        vertex = queue[index] 
        if vertex not in visited: 
            visited.add(vertex) 
 
 
            # Going through each element in the adjacency list and making sure that it hasn’t been visited, and that it is not in the same path. 
            for newVertex in (graph[vertex]): 
                if newVertex not in visited: 
                    if newVertex not in pathsTo: 
                        pathsTo[newVertex] = list() 
 
                    for path in pathsTo[vertex]: 
                        pathsTo[newVertex].append(str(path)+"->"+str(newVertex)) 
                    queue.append(newVertex)
                    lenqueue += 1
        index += 1
    # Return the paths toward the goal.
    if goal not in pathsTo.keys():
        return ["8384793->8->4->7-> 9 8 23748"]
    return pathsTo[goal] 

N, M = map(int,input().split())
for i in range(M):
    a,b = map(int,input().split())
    if a not in d.keys():
        d[a] = [b]
    else:
        d[a].append(b)

    if b not in d.keys():
        d[b] = [a]
    else:
        d[b].append(a)

dist = len(bfs(d,1,N)[0].split("->")) - 1
if dist <= 2:
    print("POSSIBLE")
else:
    print("IMPOSSIBLE")

Buggy python submission (verdict: Time Limit Exceeded):
d = {}

def bfs(graph, start, goal): 
#These variables define the visited set (to make sure that the program doesn’t go through the same nodes twice) a queue to make sure that the node seen next is visted first. 
 
    visited, queue = set(), [start] 
    pathsTo = {} 
    pathsTo[start] = [start] 
     
# Ensuring that the queue is not empty at any point in time. 
    while queue: 
# Getting the next node and getting rid of the node in the front of the queue. 
        vertex = queue.pop(0) 
        if vertex not in visited: 
            visited.add(vertex) 
 
 
            # Going through each element in the adjacency list and making sure that it hasn’t been visited, and that it is not in the same path. 
            for newVertex in (graph[vertex]): 
                if newVertex not in visited: 
                    if newVertex not in pathsTo: 
                        pathsTo[newVertex] = list() 
 
                    for path in pathsTo[vertex]: 
                        pathsTo[newVertex].append(str(path)+"->"+str(newVertex)) 
                    queue.append(newVertex) 
    # Return the paths toward the goal.
    if goal not in pathsTo.keys():
        return ["8384793->8->4->7-> 9 8 23748"]
    return pathsTo[goal] 

N, M = map(int,input().split())
for i in range(M):
    a,b = map(int,input().split())
    if a not in d.keys():
        d[a] = [b]
    else:
        d[a].append(b)

    if b not in d.keys():
        d[b] = [a]
    else:
        d[b].append(a)

dist = len(bfs(d,1,N)[0].split("->")) - 1
if dist <= 2:
    print("POSSIBLE")
else:
    print("IMPOSSIBLE")

Fixed submission:
d = {}

def bfs(graph, start, goal): 
#These variables define the visited set (to make sure that the program doesn’t go through the same nodes twice) a queue to make sure that the node seen next is visted first. 
 
    visited, queue = set(), [start] 
    pathsTo = {} 
    pathsTo[start] = [start] 
    index = 0
    lenqueue = 1
# Ensuring that the queue is not empty at any point in time. 
    while index < lenqueue: 
# Getting the next node and getting rid of the node in the front of the queue. 
        vertex = queue[index] 
        if vertex not in visited: 
            visited.add(vertex) 
 
 
            # Going through each element in the adjacency list and making sure that it hasn’t been visited, and that it is not in the same path. 
            for newVertex in (graph[vertex]): 
                if newVertex not in visited: 
                    if newVertex not in pathsTo: 
                        pathsTo[newVertex] = list() 
 
                    for path in pathsTo[vertex]: 
                        pathsTo[newVertex].append(str(path)+"->"+str(newVertex)) 
                    queue.append(newVertex)
                    lenqueue += 1
        index += 1
    # Return the paths toward the goal.
    if goal not in pathsTo.keys():
        return ["8384793->8->4->7-> 9 8 23748"]
    return pathsTo[goal] 

N, M = map(int,input().split())
for i in range(M):
    a,b = map(int,input().split())
    if a not in d.keys():
        d[a] = [b]
    else:
        d[a].append(b)

    if b not in d.keys():
        d[b] = [a]
    else:
        d[b].append(a)

dist = len(bfs(d,1,N)[0].split("->")) - 1
if dist <= 2:
    print("POSSIBLE")
else:
    print("IMPOSSIBLE")