Buggy python submission (verdict: Time Limit Exceeded):
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
to = [False]*N
for i in range(M):
  a,b = map(int, input().split())
  edge[a-1].append(b-1)
  to[b-1] = True

import sys
sys.setrecursionlimit(10**8)

def dfs(v):
  if len(edge[v])==0:
    return 1
  ans = 0
  for u in edge[v]:
    ans = max(ans, dfs(u))
  return ans+1

ans = 0
for r in range(N):
  if to[r]==False:
    ans = max(ans, dfs(r)-1)
print(ans)

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    print(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    print(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = [[] for _ in range(M)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))

Buggy python submission (verdict: Runtime Error):
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(edge[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    return ans
print(solve(edge))

Fixed submission:
import sys
sys.setrecursionlimit(100000)
N, M = map(int, input().split())
edge = [[] for _ in range(N)]
for i in range(M):
    a,b = map(int, input().split())
    edge[a-1].append(b-1)

def dp(v,dpv,e):
    if dpv[v] != -1:
        return dpv[v]
    if len(e[v])==0:
        dpv[v]=0
        return 0
    res = 0
    for w in e[v]:
        res = max(dp(w,dpv,e),res)
    res += 1
    dpv[v] = res
    return res

def solve(edge):
    dpv = [-1]*N
    for i in range(N):
        dp(i,dpv,edge)
    ans = max(dpv)
    # print(dpv)
    return ans
print(solve(edge))