from collections import defaultdict
from heapq import heapify, heappop, heappush

n, m = map(int, input().split())
Edge = defaultdict(list)
A, B = set(), set()
for _ in range(m):
    a, b = map(int, input().split())
    Edge[a - 1].append((b - 1, 2 * b - 2 * a - 1))
    A.add(a - 1)
    B.add(b - 1)
for f in A:
    for t in A:
        if f < t:
            Edge[f].append((t, 2 * (t - f)))
    Edge[f].append((n - 1, 2 * (n - 1 - f)))
for f in B:
    for t in A:
        if f < t:
            Edge[f].append((t, 2 * (t - f)))
    Edge[f].append((n - 1, 2 * (n - 1 - f)))

INF = 10**18
DP = defaultdict(lambda: INF)
DP[0] = 0
H = [(0, 0)]
heapify(H)
while H:
    ccost, cp = heappop(H)
    if ccost > DP[cp]:
        continue
    if cp == n - 1:
        print(ccost)
        break
    for np, dcost in Edge[cp]:
        if ccost + dcost >= DP[np]:
            continue
        DP[np] = ccost + dcost
        heappush(H, (ccost + dcost, np))