from collections import defaultdict
N, M = map(int, input().split())
events = set()
G = defaultdict(list)
for i in range(M):
    a, b = map(int, input().split())
    events.add(b)
    events.add(a)
    G[b].append(a)

def f(a, b):
    return 2*b - 2*a - 1

events.add(N)
dist = defaultdict(int)
dist[1] = 0
pre = 1
for pos in sorted(events):
    # posマスでは, 前のイベントマスから 2 で来るか 近道のいずれか
    memo = dist[pre] + 2*(pos - pre)
    # 近道
    for prev in G[pos]:
        memo = min(memo, dist[prev] + f(prev, pos))
    dist[pos] = memo
    pre = pos

print(dist[N])