#include <map>
#include <cstddef>

template<typename T>
class UnionFind {  
private:
  template<typename A>
  using M = std::map<T, A>;
  M<T> up; M<unsigned> size;
  T *family(T self) {
    while (up[self] != self) self = up[self];
    return &up[self]; 
  }    
  ~UnionFind() { delete up, size; }
public: 
  explicit UnionFind(size_t n): up(), size() {
    for (int i=0; i<n; i++) up[i]=i, size[i]=1;
  }
  bool connects(T a, T b) { return family(a) == family(b); }
  void connect(T a, T b) { 
    auto fa = family(a), fb = family(b);
    if (fa == fb) return;   
    auto pa = *fa, pb = *fb;
    if (size[pa] < size[pb])
         up[pa] = pb, size[pb] += size[pa];
    else up[pb] = pa, size[pa] += size[pb];
  }
}; 

#include <iostream> 
using namespace std;  
const size_t N = 1000;
int main() { int a, b;
  auto uf = new UnionFind<int>(N);
  while (cin >> a >> b) {
    if (uf->connects(a, b)) continue;
    uf->connect(a, b); cout <<a<<" "<<b<<endl;
  } 
}  

a.json b.json c.json -dump
a.json -toyaml a.yaml
x.json -path $[0].name -path $[1]