"""

"""

from sys import stdin

N,M = map(int,stdin.readline().split())

town = set()

town.add(1)
town.add(N)

lis = edge = {}

for i in range(M):

    A,B = map(int,stdin.readline().split())

    town.add(A)
    town.add(B)

    if A not in edge:
        edge[A] = []
    edge[A].append(B)

ans = {}

tl = list(town)
tl.sort()

for i in range(len(tl)):

    v = tl[i]
    
    if i == 0:
        ans[v] = 0
    else:

        lastv = tl[i-1]

        if v not in ans:
            ans[v] = float("inf")
        
        ans[v] = min(ans[v] , ans[lastv] + 2 * (v-lastv))

    if v in lis:
        for nex in lis[v]:
            if nex not in ans:
                ans[nex] = float("inf")

            ans[nex] = min(ans[nex] , ans[v] + 2*(nex-v)-1)

print (ans[N])