Buggy python submission (verdict: Time Limit Exceeded):
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range((N*3)//2):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(N//2):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)


Fixed submission:
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range((N*4)//3):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(5):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range(N):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for a,b,c in edge:
    if point[a] is not None:
        if point[b] is None:
            point[b] = point[a] + c
    point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)


Fixed submission:
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range((N*4)//3):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(5):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)

Buggy python submission (verdict: Time Limit Exceeded):
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range(N*2):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(N):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)


Fixed submission:
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range((N*4)//3):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(5):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)

Buggy python submission (verdict: Time Limit Exceeded):
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range(N*2):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(N*2):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)


Fixed submission:
N, M = map(int, input().split())
edge = []
for i in range(M):
    a,b,c = map(int, input().split())
    edge.append((a-1,b-1, c))
point = [None] * N
point[0] = 0
for i in range((N*4)//3):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
current_point = point[N-1]
for i in range(5):
    for a,b,c in edge:
        if point[a] is not None:
            if point[b] is None:
                point[b] = point[a] + c
            point[b] = max(point[b], point[a] + c)
if current_point < point[N-1]:
    print("inf")
else:
    print(current_point)