import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.numeric, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


int N;
string[] U;

int[][][] G;
int C;
int[] scc;
int[] post;

void addEdge(int u, int v) {
  G[0][u] ~= v;
  G[1][v] ~= u;
}

void dfs(int t, int u) {
  scc[u] = t ? C : -2;
  foreach (v; G[t][u]) {
    if (scc[v] == (t ? -2 : -1)) {
      dfs(t, v);
    }
  }
  if (t == 0) {
    post ~= u;
  }
}

void main() {
  try {
    for (; ; ) {
      N = readInt();
      U = new string[N];
      foreach (i; 0 .. N) {
        U[i] = readToken();
      }
      
      if (N > 52) {
        writeln("Impossible");
      } else {
        G = new int[][][](2, N * 2);
        foreach (i; 0 .. N) foreach (j; i + 1 .. N) {
          foreach (s; 0 .. 2) foreach (t; 0 .. 2) {
            if (U[i][0 .. 1 + s] == U[j][0 .. 1 + t] ||
                U[i][0 .. 1 + s] == U[j][1 + t .. 3] ||
                U[i][1 + s .. 3] == U[j][0 .. 1 + t] ||
                U[i][1 + s .. 3] == U[j][1 + t .. 3]) {
              addEdge(i * 2 + s, j * 2 + (t ^ 1));
              addEdge(j * 2 + t, i * 2 + (s ^ 1));
            }
          }
        }
        C = 0;
        scc = new int[N * 2];
        scc[] = -1;
        post = [];
        foreach (u; 0 .. N * 2) {
          if (scc[u] == -1) {
            dfs(0, u);
          }
        }
        foreach_reverse (u; post) {
          if (scc[u] == -2) {
            dfs(1, u);
            ++C;
          }
        }
        bool ans = true;
        foreach (i; 0 .. N) {
          ans = ans && (scc[i * 2] != scc[i * 2 + 1]);
        }
        if (ans) {
          foreach (i; 0 .. N) {
            const s = (scc[i * 2] > scc[i * 2 + 1]) ? 0 : 1;
            writeln(U[i][0 .. 1 + s], " ", U[i][1 + s .. 3]);
          }
        } else {
          writeln("Impossible");
        }
      }
    }
  } catch (EOFException e) {
  }
}