from heapq import heappush, heappop
INF=10**18
def dijkstra():
  dist=defaultdict(lambda:INF)
  hq=[(0,1)]
  dist[1]=0
  seen=set()
  while hq:
    w,v=heappop(hq)
    if dist[v]<w:
      continue
    seen.add(v)
    for to,cost in edge[v]:
      if to not in seen and dist[v]+cost<dist[to]:
        dist[to]=dist[v]+cost
        heappush(hq,(dist[to],to))
  return dist

from collections import defaultdict
edge=defaultdict(list)
n,m=map(int,input().split())
town=set([1,n])
for _ in range(m):
  a,b=map(int,input().split())
  town.add(a)
  town.add(b)
  edge[a].append((b,2*b-2*a-1))

town=sorted(list(town))
k=len(town)
for i in range(k-1):
  edge[town[i]].append((town[i+1],2*(town[i+1]-town[i])))
#print(edge)
d=dijkstra()
print(d[n])