Buggy python submission (verdict: Runtime Error):
import sys

N, M = [int(s) for s in input().split()]
sys.setrecursionlimit(N)
dp = [-1] * (N+1)
neighbors = [[] for _ in range(N+1)]

for _ in range(M):
    x, y = [int(s) for s in input().split()]
    neighbors[x].append(y)

def LP(v):
    if dp[v] != -1:
        return dp[v]
    else:
        res = 0
        lp = [-1]
        for nv in neighbors[v]:
            lp.append(LP(nv))
        res = max(res, max(lp) + 1)
        dp[v] = res
        return res

ans = 0
for v in range(1,N+1):
    ans = max(ans, LP(v))

print(ans)



Fixed submission:
import sys

N, M = [int(s) for s in input().split()]
sys.setrecursionlimit(10**5)
dp = [-1] * (N+1)
neighbors = [[] for _ in range(N+1)]

for _ in range(M):
    x, y = [int(s) for s in input().split()]
    neighbors[x].append(y)

def LP(v):
    if dp[v] != -1:
        return dp[v]
    else:
        res = 0
        lp = [-1]
        for nv in neighbors[v]:
            lp.append(LP(nv))
        res = max(res, max(lp) + 1)
        dp[v] = res
        return res

ans = 0
for v in range(1,N+1):
    ans = max(ans, LP(v))

print(ans)

Buggy python submission (verdict: Runtime Error):
N, M = [int(s) for s in input().split()]

dp = [-1] * (N+1)
neighbors = [[] for _ in range(N+1)]

for _ in range(M):
    x, y = [int(s) for s in input().split()]
    neighbors[x].append(y)

def LP(v):
    if dp[v] != -1:
        return dp[v]
    else:
        res = 0
        lp = [-1]
        for nv in neighbors[v]:
            lp.append(LP(nv))
        res = max(res, max(lp) + 1)
        dp[v] = res
        return res

ans = 0
for v in range(1,N+1):
    ans = max(ans, LP(v))

print(ans)



Fixed submission:
import sys

N, M = [int(s) for s in input().split()]
sys.setrecursionlimit(10**5)
dp = [-1] * (N+1)
neighbors = [[] for _ in range(N+1)]

for _ in range(M):
    x, y = [int(s) for s in input().split()]
    neighbors[x].append(y)

def LP(v):
    if dp[v] != -1:
        return dp[v]
    else:
        res = 0
        lp = [-1]
        for nv in neighbors[v]:
            lp.append(LP(nv))
        res = max(res, max(lp) + 1)
        dp[v] = res
        return res

ans = 0
for v in range(1,N+1):
    ans = max(ans, LP(v))

print(ans)

Buggy python submission (verdict: Runtime Error):
N, M = [int(s) for s in input().split()]

dp = [-1] * (N+1)
neighbors = [[] for _ in range(1,N+1)]

for _ in range(M):
    x, y = [int(s) for s in input().split()]
    neighbors[x].append(y)

def LP(v):
    if dp[v] != -1:
        return dp[v]
    else:
        res = 0
        lp = []
        for nv in neighbors[v]:
            lp.append(LP(nv))
        res = max(res, max(lp) + 1)
        dp[v] = res
        return res

ans = 0
for v in range(1,N+1):
    ans = max(ans, LP(v))

print(ans)



Fixed submission:
import sys

N, M = [int(s) for s in input().split()]
sys.setrecursionlimit(10**5)
dp = [-1] * (N+1)
neighbors = [[] for _ in range(N+1)]

for _ in range(M):
    x, y = [int(s) for s in input().split()]
    neighbors[x].append(y)

def LP(v):
    if dp[v] != -1:
        return dp[v]
    else:
        res = 0
        lp = [-1]
        for nv in neighbors[v]:
            lp.append(LP(nv))
        res = max(res, max(lp) + 1)
        dp[v] = res
        return res

ans = 0
for v in range(1,N+1):
    ans = max(ans, LP(v))

print(ans)