from collections import defaultdict

def dfs(now: int, prev: int):
    for nxt in g[now]:
        if nxt == prev:
            continue
        dist[nxt] = max(dist[nxt], dist[now] + 1)
        dfs(nxt, now)

n, m = map(int, input().split())

g_rev = defaultdict(list)
g = defaultdict(list)
visited = set()
for _ in range(m):
    a, b = map(int, input().split())
    visited.add(a)
    visited.add(b)
    g[a].append(b)
    g_rev[b].append(a)

visited = list(visited)
s_list = []
dist = defaultdict(lambda : -10 ** 18)
for start in visited:
    if g_rev[start] == []:
        s_list.append(start)
        dist[start] = 0

for start in s_list:
    dfs(start, -1)

num = 0
for k, v in dist.items():
    num = max(num, v)

print(2 * (n - 1) - num)