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])