#import<bits/stdc++.h>
#define c(a,b)(a=a>b?a:b)
long n,m,h[1<<17],G[1<<17],i,u,v,p[1<<18],q;main(){for(;std::cin>>v;)n?m?++i<n?h[i]=v:i-n&1?h[u]<h[v]?:u^=v^=u^=v,G[i-n]=h[u]*n*n+u*n+v:u=v:m=v:n=v+1;std::sort(G,G+2*m);p[1]=p[2*n-1]=n;for(i=m;m=G[i++];)c(q,c(p[v=m%n],p[u=m/n%n]+1)+c(p[v+n],p[u+n]+1)-2*n+2);printf("%d\n",q-1);}