ll@n,@m,l[n+2],z=0;
rd(((l+1))(n));
l[0]=-ll_inf;
l[n+1]=ll_inf;
rep(m){
	ll@f,@b,@w;
	ll i=bsearch_min[ll,i,0,n+2](l[i]>=f);
	z+=max(b,w+l[i-1]-f,w-l[i]+f);
}
wt(z);