spfa+差分约束

from collections import deque
n, m = map(int, input().split())
g = [[] for i in range(n + 1)]
for i in range(m):
    a, b = map(int, input().split())
    g[b].append((a, 1))
for i in range(1, n + 1):
    g[0].append((i, 100))
dist = [float('-inf')] * (n + 1)
dist[0] = 0
cnt = [0] * (n + 1)
st = [False] * (n + 1)
def spfa():
    q = deque()
    q.append(0)
    st[0] = True
    while q:
        i = q.popleft()
        st[i] = False
        for j, d in g[i]:
            if dist[j] < dist[i] + d:
                dist[j] = dist[i] + d 
                cnt[j] = cnt[i] + 1 
                if cnt[j] >= n + 1:
                    return True
                if not st[j]:
                    st[j] = True
                    q.append(j)
    return False

if spfa():
    print("Poor Xed")
else:
    print(sum(dist))