#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
#define ll long long
#define ul unsigned long long
#define N 100010
char getc(){char c=getchar();while ((c<'A'||c>'Z')&&(c<'a'||c>'z')&&(c<'0'||c>'9')) c=getchar();return c;}
int gcd(int n,int m){return m==0?n:gcd(m,n%m);}
int read()
{int x=0,f=1;char c=getchar();while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();return x*f;
}
int n,ans,f[N],g[N];
struct tree
{int p[N],t,size[N],root;ul hax[N],f[N];struct data{int to,nxt;}edge[N<<1];void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}void dfs(int k,int from){size[k]=1;for (int i=p[k];i;i=edge[i].nxt)if (edge[i].to!=from)dfs(edge[i].to,k),size[k]+=size[edge[i].to];}int findroot(int k,int s){int mx=0;for (int i=p[k];i;i=edge[i].nxt)if (size[edge[i].to]<size[k]&&size[edge[i].to]>size[mx]) mx=edge[i].to;if (size[mx]*2>s) return findroot(mx,s);else return k;}void refind(){for (int i=p[root];i;i=edge[i].nxt)if (size[edge[i].to]*2>=size[root]) {root=edge[i].to;break;}}void gethash(int k,int from){for (int i=p[k];i;i=edge[i].nxt)if (edge[i].to!=from) gethash(edge[i].to,k);int cnt=0;for (int i=p[k];i;i=edge[i].nxt)if (edge[i].to!=from) f[++cnt]=hax[edge[i].to];sort(f+1,f+cnt+1);hax[k]=0;for (int i=1;i<=cnt;i++) hax[k]=hax[k]*107+f[i];hax[k]+=size[k]*509;}
}a,b;
bool cmp(const int&x,const int&y)
{return a.hax[x]<a.hax[y];
}
bool cmp2(const int&x,const int&y)
{return b.hax[x]<b.hax[y]||b.hax[x]==b.hax[y]&&x>y;
}
void work(int x,int y)
{int cnt=0,cnt2=0;for (int i=a.p[x];i;i=a.edge[i].nxt)if (a.size[a.edge[i].to]<a.size[x]) f[++cnt]=a.edge[i].to; for (int i=b.p[y];i;i=b.edge[i].nxt)if (b.size[b.edge[i].to]<b.size[y]) g[++cnt2]=b.edge[i].to; sort(f+1,f+cnt+1,cmp);sort(g+1,g+cnt2+1,cmp2);if (cnt>cnt2||cnt2>cnt+1) return;if (cnt2==cnt+1){int t=0;for (int i=1,j=1;i<=cnt2;i++,j++)if (a.hax[f[j]]!=b.hax[g[i]]||j>cnt) if (!t) t=g[i++];else return;if (t) ans=min(ans,t);return;}if (cnt2==cnt){int u,v;for (u=1;u<=cnt;u++) if (a.hax[f[u]]!=b.hax[g[u]]) break;if (!u) return;if (a.hax[f[u]]<b.hax[g[u]]) for (v=u;v<cnt;v++) if (a.hax[f[v+1]]!=b.hax[g[v]]) break;if (!v) return;for (int i=v+1;i<=cnt;i++) if (a.hax[f[i]]!=b.hax[g[i]]) return;for (int i=1;i<=cnt;i++) if (b.hax[g[v]]==b.hax[g[i]]) work(f[u],g[i]);}
}
int main()
{
#ifndef ONLINE_JUDGEfreopen("bzoj4754.in","r",stdin);freopen("bzoj4754.out","w",stdout);const char LL[]="%I64d\n";
#elseconst char LL[]="%lld\n";
#endifn=read();ans=n+1;for (int i=1;i<n;i++){int x=read(),y=read();a.addedge(x,y),a.addedge(y,x);}for (int i=1;i<=n;i++){int x=read(),y=read();b.addedge(x,y),b.addedge(y,x);}a.dfs(1,1),b.dfs(1,1);a.root=a.findroot(1,n),b.root=b.findroot(1,n+1);a.dfs(a.root,a.root),b.dfs(b.root,b.root);a.gethash(a.root,a.root),b.gethash(b.root,b.root);work(a.root,b.root);if (n&1) a.refind();else b.refind();a.dfs(a.root,a.root),b.dfs(b.root,b.root);a.gethash(a.root,a.root),b.gethash(b.root,b.root);work(a.root,b.root);cout<<ans;return 0;
}