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)

INF = 10**18
DP = defaultdict(lambda: INF)
DP[0] = 0
H = [(0, 0)]
visited = set()
heapify(H)
while H:
    ccost, cp = heappop(H)
    if ccost > DP[cp] or cp in visited:
        continue
    if cp == n - 1:
        print(ccost)
        break
    visited.add(cp)
    seen = set()
    for np, dcost in Edge[cp]:
        seen.add(np)
        if ccost + dcost >= DP[np]:
            continue
        DP[np] = ccost + dcost
        heappush(H, (ccost + dcost, np))
    for np in A:
        if np in seen:
            continue
        if cp >= np:
            continue
        if ccost + 2 * (np - cp) >= DP[np]:
            continue
        DP[np] = ccost + 2 * (np - cp)
        heappush(H, (ccost + 2 * (np - cp), np))
    if ccost + 2 * (n - 1 - cp) < DP[n - 1]:
        DP[n - 1] = ccost + 2 * (n - 1 - cp)
        heappush(H, (ccost + 2 * (n - 1 - cp), n - 1))