#include <bits/stdc++.h>
using namespace std;

#define _p(...) (void)printf(__VA_ARGS__)
#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()
#define bit(n) (1LL<<(n))
#define sz(x) ((int)(x).size())
#define fst first
#define snd second
using ll=long long;using pii=pair<int,int>;
using vb=vector<bool>;using vs=vector<string>;
using vi=vector<int>;using vvi=vector<vi>;using vvvi=vector<vvi>;
using vl=vector<ll>;using vvl=vector<vl>;using vvvl=vector<vvl>;
using vd=vector<double>;using vvd=vector<vd>;using vvvd=vector<vvd>;
using vpii=vector<pii>;using vvpii=vector<vpii>;using vvvpii=vector<vvpii>;
template<typename T>T read(){T t;cin>>t;return t;}
template<class T,class U>ostream&operator<<(ostream&o,const pair<T,U>&p){o<<'('<<p.fst<<", "<<p.snd<<')';return o;}

void panic() {
  cout << "Impossible" << endl;
  exit(0);
}

int n;
map<string, int> fix;
vector<int> ans;
set<string> used;
vector<string> s1;
vector<string> s2;
vector<string> s3;
vector<string> s4;

void output() {
  rep(i, n) {
    if (ans[i] == 12) {
      cout << s1[i] << ' ' << s2[i] << endl;
    }
    else if (ans[i] == 34) {
      cout << s3[i] << ' ' << s4[i] << endl;
    }
    else {
      assert(false);
    }
  }
  exit(0);
}

void backtrack(int i) {
  if (i >= n) {
    output();
  }
  if (ans[i] != -1) backtrack(i + 1);

  if (used.count(s1[i]) == 0 && used.count(s2[i]) == 0) {
    if ((fix.count(s1[i]) == 0 || fix[s1[i]] == i) && (fix.count(s2[i]) == 0 || fix[s2[i]] == i)) {
      used.insert(s1[i]);
      used.insert(s2[i]);
      ans[i] = 12;
      backtrack(i+1);
      ans[i] = -1;
      used.erase(s1[i]);
      used.erase(s2[i]);
    }
  }

  if (used.count(s3[i]) == 0 && used.count(s4[i]) == 0) {
    if ((fix.count(s3[i]) == 0 || fix[s4[i]] == i) && (fix.count(s3[i]) == 0 || fix[s4[i]] == i)) {
      used.insert(s3[i]);
      used.insert(s4[i]);
      ans[i] = 34;
      backtrack(i+1);
      ans[i] = -1;
      used.erase(s3[i]);
      used.erase(s4[i]);
    }
  }
}

void Main() {
  n = read<int>();
  ans.resize(n, -1);

  rep(i, n) {
    string s = read<string>();
    s1.push_back(s.substr(0, 1));
    s2.push_back(s.substr(1, 2));
    s3.push_back(s.substr(0, 2));
    s4.push_back(s.substr(2, 1));

    if (s[0] == s[2]) {
      if (s[0] == s[1]) {
        if (fix.count(s1[i])) panic();
        if (fix.count(s2[i])) panic();
        fix.emplace(s1[i], i);
        fix.emplace(s2[i], i);
        used.insert(s1[i]);
        used.insert(s2[i]);
        ans[i] = 12;
      }
      else {
        if (fix.count(s1[i])) panic();
        fix.emplace(s1[i], i);
      }
    }
  }

  //cout << "s1:"; rep(ii,sz(s1)) cout << ' ' << s1[ii]; cout << endl;
  //cout << "s2:"; rep(ii,sz(s2)) cout << ' ' << s2[ii]; cout << endl;
  //cout << "s3:"; rep(ii,sz(s3)) cout << ' ' << s3[ii]; cout << endl;
  //cout << "s4:"; rep(ii,sz(s4)) cout << ' ' << s4[ii]; cout << endl;
  //forr(si, fix) cout << si.fst << ", " << si.snd << endl;

  backtrack(0);

  panic();
}
int main() { cin.tie(nullptr); ios::sync_with_stdio(false); Main(); return 0; }