#include<bits/stdc++.h>
using namespace std;
const int mod=998244353;
int n,cnt,ans=1;
bool vis[1000005];
vector<int>e[1000005];
void dfs(int pos){vis[pos]=1,cnt+=2-e[pos].size();for(auto v:e[i])if(!vis[v])dfs(v);}
int main(){
  ios::sync_with_stdio(0),cin.tie(0),cin>>n;
  for(int i=1,u,v;i<=2*n-2;i++){cin>>u>>v;if(u==v)return puts("0"),0;if(u>v)swap(u,v);e[u].push_back(v+n-2),e[v+n-2].push_back(u);}
  for(int i=1;i<=2*n-2;i++){if(!vis[i]){cnt=0,dfs(i);if(cnt)return puts("0"),0;ans=2ll*ans%mod;}}
  return cout<<ans<<'\n',0;
}

answer.code: In function ‘void dfs(int)’:
answer.code:7:64: error: ‘i’ was not declared in this scope
    7 | void dfs(int pos){vis[pos]=1,cnt+=2-e[pos].size();for(auto v:e[i])if(!vis[v])dfs(v);}
      |                                                                ^