compress = lambda arr: {e: i for i, e in enumerate(sorted(set(arr)))}
n, m = map(int, input().split())
t = (n - 1) * 2
a = [0] * m
b = [0] * m
for i in range(m):
    a[i], b[i] = map(int, input().split())
cp = compress([1] + a + b + [n])
n = len(cp)
g = [[] for _ in range(n)]
for i in range(m):
    g[cp[a[i]]].append(cp[b[i]])
dp = [0] * n
for i in range(n - 1):
    dp[i + 1] = max(dp[i + 1], dp[i])
    for j in g[i]:
        dp[j] = max(dp[j], dp[i] + 1)
print(t - dp[n - 1])