```cpp
#include<bits/stdc++.h>
using namespace std;
struct s{
int ll,rr;
}a[1000001];
int qian(int k){
cout<<char(k+'a'-1);
if(a[k].ll) qian(a[k].ll);
if(a[k].rr) qian(a[k].rr);
}
int root=1;
int n;
string s;
bool f[1000001];
int main(){
cin>>n;
for(int i=1;i<=n;i++){
cin>>s;
if(s[1]!='*'){
a[s[0]-'a'+1].ll=s[1]-'a'+1;
f[s[1]-'a'+1]=true;
}
if(s[2]!='*'){
a[s[0]-'a'+1].rr=s[2]-'a'+1;
f[s[2]-'a'+1]=true;
}
}
for(root=1;f[root];root++);
qian(root);
cout<<endl;
return 0;
}
```
by iakioi114514 @ 2023-04-20 19:20:21