#include<bits/stdc++.h>
#define int long long
const int inf=8938103643641919514ll;
const int mod=1000000007;
const int dd[]={0,-1,0,1,0};
using namespace std;
int a,b,c,d;
char p[100000][3];
unordered_set<string> se;
vector<string> ve;
void saiki(int u){
	if(u==a){
		for(int i=0;i<a;i++)
			cout<<ve[i*2]<<" "<<ve[i*2+1]<<endl;;
		exit(0);
	}
	string s,t;
	s.push_back(p[u][0]);
	t.push_back(p[u][1]);
	t.push_back(p[u][2]);
	if(se.find(s)==end(se)&&se.find(t)==end(se)){
		se.insert(s);
		se.insert(t);
		ve.push_back(s);
		ve.push_back(t);
		saiki(u+1);
		se.erase(s);
		se.erase(t);
		ve.resize(ve.size()-2);
	}
	s.clear();
	t.clear();
	s.push_back(p[u][0]);
	s.push_back(p[u][1]);
	t.push_back(p[u][2]);
	if(se.find(s)==end(se)&&se.find(t)==end(se)){
		se.insert(s);
		se.insert(t);
		ve.push_back(s);
		ve.push_back(t);
		saiki(u+1);
		se.erase(s);
		se.erase(t);
		ve.resize(ve.size()-2);
	}
}
signed main(){
	int i,j;
	cin>>a;
	for(i=0;i<a;i++)
		cin>>p[i];
	saiki(0);
	cout<<"Impossible"<<endl;
}