INF = 10**18
from collections import defaultdict
N, M = map(int, input().split())
G = defaultdict(list)
events = []

def chmax(DP,i,v):
    if DP[i] < v: DP[i] = v
def chmin(DP,i,v):
    if DP[i] > v: DP[i] = v

for i in range(M):
    a, b = map(int, input().split())
    G[a].append(b)
    events.append(a)
    events.append(b)

events.sort()
if N not in events:
    events.append(N)

dp = defaultdict(lambda: INF)
dp[1] = 0
# 確定マスのうち一番大きいもの
pre = 1

for masu in events:

    # pre から近道無しで来た場合
    option1 = dp[pre] + (masu - pre)*2
    #option2 = INF

    # 近道で masu まで来る経路がある場合
    #if masu in dp:
    #    option2 = dp[masu]
    
    #dp[masu] = min(option1, option2)
    chmin(dp, masu, option1)


    # 近道で このさきのマスへの経路がある場合は蒔いておく
    for nex in G[masu]:
        # dp[nex] = min(dp[nex], dp[masu] + (2*nex - 2*masu - 1)
        chmin(dp, nex, dp[masu] + (2*nex - 2*masu - 1))

    pre = masu

ans = dp[N]
print(ans)