Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline
from collections import deque
from copy import deepcopy
def main():
    N, M, P = map( int, input().split())
    d = dict()
    E = [[] for _ in range(N)]
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        d[(a,b)] = c-P
        E[b].append(a)
    G = [False]*N
    G[N-1] = True
    q = deque([N-1])
    while q:
        v = q.popleft()
        for w in E[v]:
            if G[w] == False:
                G[w] = True
                q.append(w)
    V = [None]*N
    V[0] = 0
    I = sum([1 for i in range(N) if G[i] == True])
    for _ in range(I-1):
        for (s,t), cost in d.items():
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    W = deepcopy(V) #[ V[i] for i in range(N)]
    for _ in range(I-1):
        for (s,t), cost in d.items(): #d.keys()
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + d[e] > V[t]:
                V[t] = V[s] + cost
    for i in range(N):
        if W[i] == None or G[t] == False:
            continue
        if V[i] > W[i]:
            print(-1)
            return

    print( max(W[-1], 0))
if __name__ == '__main__':
    main()


Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
from copy import deepcopy
def main():
    N, M, P = map( int, input().split())
    E = []
    rE = [[] for _ in range(N)]
    
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        E.append((a,b,c-P))
        rE[b].append(a)
    # 頂点Nに到達する頂点
    G = [False]*N
    G[N-1] = True
    q = deque([N-1])
    while q:
        v = q.popleft()
        for w in rE[v]:
            if G[w] == False:
                G[w] = True
                q.append(w)
    # Bellman-Ford
    V = [None]*N
    V[0] = 0
    I = sum([1 for i in range(N) if G[i] == True])
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    W = deepcopy(V) #[ V[i] for i in range(N)]
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    for i in range(N):
        if W[i] == None or G[i] == False:
            continue
        if V[i] > W[i]: # 頂点iは、頂点Nに到達するので、負（正？）閉路は伝播する
            print(-1)
            return

    print( max(W[-1], 0))
if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

def main():
    N, M, P = map( int, input().split())
    d = dict()
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        d[(a,b)] = P-c

    V = [None]*N
    V[0] = 0
    for _ in range(N-1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    W = [V[i] for i in range(N)]
    for e in d:
        s, t = e
        if V[s] == None:
            continue
        if V[t] == None:
            V[t] = V[s] + d[e]
            continue
        if V[s] + d[e] < V[t]:
            V[t] = V[s] + d[e]
    for i in range(N):
        if V[i] == None or W[i] == None:
            continue
        if V[i] < W[i]:
            V[i] = "a"
    for _ in range(N):
        for e in d:
            s, t = e
            if V[s] == "a" or V[t] == a:
                V[t] == "a"
                continue
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    # ans = V[N-1]
    # for _ in range(N):
    #     for e in d:
    #         s, t = e
    #         if V[s] + d[e] < V[t]:
    #             V[t] = V[s] + d[e]

    # if V[N-1] < ans:
    #     print(-1)
    #     return
    # print( max(-ans,0))
    if V[-1] == "a":
        print(-1)
    else:
        print(max(-W[-1],0))
if __name__ == '__main__':
    main()


Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
from copy import deepcopy
def main():
    N, M, P = map( int, input().split())
    E = []
    rE = [[] for _ in range(N)]
    
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        E.append((a,b,c-P))
        rE[b].append(a)
    # 頂点Nに到達する頂点
    G = [False]*N
    G[N-1] = True
    q = deque([N-1])
    while q:
        v = q.popleft()
        for w in rE[v]:
            if G[w] == False:
                G[w] = True
                q.append(w)
    # Bellman-Ford
    V = [None]*N
    V[0] = 0
    I = sum([1 for i in range(N) if G[i] == True])
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    W = deepcopy(V) #[ V[i] for i in range(N)]
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    for i in range(N):
        if W[i] == None or G[i] == False:
            continue
        if V[i] > W[i]: # 頂点iは、頂点Nに到達するので、負（正？）閉路は伝播する
            print(-1)
            return

    print( max(W[-1], 0))
if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

def main():
    N, M, P = map( int, input().split())
    d = dict()
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        d[(a,b)] = P-c

    V = [None]*N
    V[0] = 0
    for _ in range(N-1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    W = [V[i] for i in range(N)]
    for _ in range(1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    for i in range(N):
        if V[i] < W[i]:
            V[i] = -10**14*2
    for _ in range(1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    # ans = V[N-1]
    # for _ in range(N):
    #     for e in d:
    #         s, t = e
    #         if V[s] + d[e] < V[t]:
    #             V[t] = V[s] + d[e]

    # if V[N-1] < ans:
    #     print(-1)
    #     return
    # print( max(-ans,0))
    if V[-1] <= -10**14:
        print(-1)
    else:
        print(max(-V[-1],0))
if __name__ == '__main__':
    main()


Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
from copy import deepcopy
def main():
    N, M, P = map( int, input().split())
    E = []
    rE = [[] for _ in range(N)]
    
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        E.append((a,b,c-P))
        rE[b].append(a)
    # 頂点Nに到達する頂点
    G = [False]*N
    G[N-1] = True
    q = deque([N-1])
    while q:
        v = q.popleft()
        for w in rE[v]:
            if G[w] == False:
                G[w] = True
                q.append(w)
    # Bellman-Ford
    V = [None]*N
    V[0] = 0
    I = sum([1 for i in range(N) if G[i] == True])
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    W = deepcopy(V) #[ V[i] for i in range(N)]
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    for i in range(N):
        if W[i] == None or G[i] == False:
            continue
        if V[i] > W[i]: # 頂点iは、頂点Nに到達するので、負（正？）閉路は伝播する
            print(-1)
            return

    print( max(W[-1], 0))
if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

def main():
    N, M, P = map( int, input().split())
    d = dict()
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        d[(a,b)] = P-c

    V = [None]*N
    V[0] = 0
    for _ in range(N-1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    W = [V[i] for i in range(N)]
     for _ in range(1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    for i in range(N):
        if V[i] < W[i]:
            V[i] = -10**14*2
    for _ in range(1):
        for e in d:
            s, t = e
            if V[s] == None:
                continue
            if V[t] == None:
                V[t] = V[s] + d[e]
                continue
            if V[s] + d[e] < V[t]:
                V[t] = V[s] + d[e]
    # ans = V[N-1]
    # for _ in range(N):
    #     for e in d:
    #         s, t = e
    #         if V[s] + d[e] < V[t]:
    #             V[t] = V[s] + d[e]

    # if V[N-1] < ans:
    #     print(-1)
    #     return
    # print( max(-ans,0))
    if V[-1] <= -10**14:
        print(-1)
    else:
        print(max(-V[-1],0))
if __name__ == '__main__':
    main()


Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
from copy import deepcopy
def main():
    N, M, P = map( int, input().split())
    E = []
    rE = [[] for _ in range(N)]
    
    for _ in range(M):
        a, b, c = map( int, input().split())
        a, b = a-1, b-1
        E.append((a,b,c-P))
        rE[b].append(a)
    # 頂点Nに到達する頂点
    G = [False]*N
    G[N-1] = True
    q = deque([N-1])
    while q:
        v = q.popleft()
        for w in rE[v]:
            if G[w] == False:
                G[w] = True
                q.append(w)
    # Bellman-Ford
    V = [None]*N
    V[0] = 0
    I = sum([1 for i in range(N) if G[i] == True])
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    W = deepcopy(V) #[ V[i] for i in range(N)]
    for _ in range(I-1):
        for s, t, cost in E:
            if V[s] == None or G[t] == False:
                continue
            if V[t] == None:
                V[t] = V[s] + cost
                continue
            if V[s] + cost > V[t]:
                V[t] = V[s] + cost
    for i in range(N):
        if W[i] == None or G[i] == False:
            continue
        if V[i] > W[i]: # 頂点iは、頂点Nに到達するので、負（正？）閉路は伝播する
            print(-1)
            return

    print( max(W[-1], 0))
if __name__ == '__main__':
    main()