#include<iostream>
using namespace std;
int n;char start;
struct node{
	char l,r;
}tree[30]/*using:-96*/;
void dfs(char x){
	cout<<x;
	if(tree[x-96].l!='*') dfs(tree[x-96].l);
	if(tree[x-96].r!='*') dfs(tree[x-96].r);
} 
int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		char jd,l,r;
		cin>>jd>>tree[int(jd)-96].l>>tree[int(jd)-96].r;
		if(i==0) start=jd;
	}
	dfs(start);
}

求大佬解答