#import<bits/stdc++.h>
using namespace std;long n,m,h,i,u,x[1<<17],k;vector<long>G[1<<17],p(1<<18,-1e9);main(){for(;cin>>h;)n?m?i<n?x[i++]=h*n+i:i++-n&1?x[--u]>x[--h]?:u^=h^=u^=h,G[u].push_back(h),0:u=h:m=h:n=h;sort(x,x+n);for(p[i=0]=p[2*n-1]=1;i<2*n;i++)for(int j:G[u=x[i%n]%n])h=i/n*n,k=max(k,p[u+n-h]+(p[u+h]=max(p[u+h],p[j+h]+1)));cout<<k-1<<"\n";}