Buggy python submission (verdict: Time Limit Exceeded):
N, M = map(int, input().split())
adjacent = []
score = ['None' for i in range(N)]
score[0] = 0
for i in range(M):
    a, b, c = map(int, input().split())
    adjacent.append([a-1, b-1, c])
for i in range(2*N):
    for j in adjacent:
      if score[j[1]] == 'None' and score[j[0]] != 'None':
        score[j[1]] = score[j[0]] + j[2]
      if score[j[1]] != 'None' and score[j[0]] != 'None':
        if score[j[1]] < score[j[0]] + j[2]:
          score[j[1]] = score[j[0]] + j[2]
    if i == N-2:
      t = score[N-1]
    if i == 2*N-1:
      if t != score[N-1]:
        score[N-1] = 1e+15
if score[N-1] < 1e+15:
    print(t)
else:
    print('inf')

Fixed submission:
N, M = map(int, input().split())
adjacent = []
score = ['None' for i in range(N)]
score[0] = 0
for i in range(M):
    a, b, c = map(int, input().split())
    adjacent.append([a-1, b-1, c])
for i in range(N):
    for j in adjacent:
      if score[j[1]] == 'None' and score[j[0]] != 'None':
        score[j[1]] = score[j[0]] + j[2]
      if score[j[1]] != 'None' and score[j[0]] != 'None':
        if score[j[1]] < score[j[0]] + j[2]:
          score[j[1]] = score[j[0]] + j[2]
    if i == N-2:
      t = score[N-1]
    if i == N-1:
      if t != score[N-1]:
        score[N-1] = 1e+15
if score[N-1] < 1e+15:
    print(t)
else:
    print('inf')

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
adjacent = []
score = ['None' for i in range(N)]
score[0] = 0
for i in range(M):
    a, b, c = map(int, input().split())
    adjacent.append([a-1, b-1, c])
for i in range(2N):
    for j in adjacent:
      if score[j[1]] == 'None' and score[j[0]] != 'None':
        score[j[1]] = score[j[0]] + j[2]
      if score[j[1]] != 'None' and score[j[0]] != 'None':
        if score[j[1]] < score[j[0]] + j[2]:
          score[j[1]] = score[j[0]] + j[2]
    if i == N-1:
      t = score[N-1]
    if i == 2N:
      if t != score[N-1]:
        score[N-1] = 1e+15
if score[N-1] < 1e+15:
    print(score[N-1])
else:
    print('inf')


Fixed submission:
N, M = map(int, input().split())
adjacent = []
score = ['None' for i in range(N)]
score[0] = 0
for i in range(M):
    a, b, c = map(int, input().split())
    adjacent.append([a-1, b-1, c])
for i in range(N):
    for j in adjacent:
      if score[j[1]] == 'None' and score[j[0]] != 'None':
        score[j[1]] = score[j[0]] + j[2]
      if score[j[1]] != 'None' and score[j[0]] != 'None':
        if score[j[1]] < score[j[0]] + j[2]:
          score[j[1]] = score[j[0]] + j[2]
    if i == N-2:
      t = score[N-1]
    if i == N-1:
      if t != score[N-1]:
        score[N-1] = 1e+15
if score[N-1] < 1e+15:
    print(t)
else:
    print('inf')

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
adjacent = []
score = ['None' for i in range(N)]
score[0] = 0
for i in range(M):
    a, b, c = map(int, input().split())
    adjacent.append([a-1, b-1, c])
for i in range(N-1):
    for j in adjacent:
      if score[j[1]] == 'None' and score[j[0]] != 'None':
        score[j[1]] = score[j[0]] + j[2]
      if score[j[1]] != 'None' and score[j[0]] != 'None':
        if score[j[1]] < score[j[0]] + j[2]:
          score[j[1]] = score[j[0]] + j[2]
for j in adjacent:
    if score[j[1]] < score[j[0]] + j[2]:
        score[N-1] = 1e+15
if score[N-1] < 1e+15:
    print(score[N-1])
else:
    print('inf')

Fixed submission:
N, M = map(int, input().split())
adjacent = []
score = ['None' for i in range(N)]
score[0] = 0
for i in range(M):
    a, b, c = map(int, input().split())
    adjacent.append([a-1, b-1, c])
for i in range(N):
    for j in adjacent:
      if score[j[1]] == 'None' and score[j[0]] != 'None':
        score[j[1]] = score[j[0]] + j[2]
      if score[j[1]] != 'None' and score[j[0]] != 'None':
        if score[j[1]] < score[j[0]] + j[2]:
          score[j[1]] = score[j[0]] + j[2]
    if i == N-2:
      t = score[N-1]
    if i == N-1:
      if t != score[N-1]:
        score[N-1] = 1e+15
if score[N-1] < 1e+15:
    print(t)
else:
    print('inf')