#include <bits/stdc++.h>
using namespace std;
 
int main() {
	// your code goes here
	int n;cin>>n;
	int a[n][2];
	for(int i=0;i<n;i++){
		for(int j=0;j<2;j++){
			cin>>a[i][j];
		}
	}
	vector<int>adj[n];
	for(int i=0;i<n;i++){
            for(int j=0;j<2;j++){
                adj[i].push_back(j);
                adj[j].push_back(i);
            }
     }
     for(auto i:a){
     //	cout<<i<<"-"<<"\n";
     	cout<<i[0]<<" "<<i[1];
     }
	return 0;
}

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MwowIDEgCjEgMgoyIDA=

3
0 1 
1 2
2 0