import java.io.*;
import java.math.*;
import java.util.*;

import static java.util.Arrays.*;

public class _470 {
	private static final int mod = (int)1e9+7;

	final Random random = new Random(0);
	final IOFast io = new IOFast();

	/// MAIN CODE
	public void run() throws IOException {
//		int TEST_CASE = Integer.parseInt(new String(io.nextLine()).trim());
		int TEST_CASE = 1;
		while(TEST_CASE-- != 0) {
			int n = io.nextInt();
			
			if (n > 52) {
				io.out.println("Impossible");
				return;
			}
			
			Sat2 sat = new Sat2(2*n);
			String[][][] cs = new String[n][2][2];
			for (int i = 0; i < n; i++) {
				String s = io.nextString();
				cs[i][0][0] = s.substring(0, 1);
				cs[i][0][1] = s.substring(1, 3);
				cs[i][1][0] = s.substring(2, 3);
				cs[i][1][1] = s.substring(0, 2);
				sat.Or(sat.Not(2*i+0), sat.Not(2*i+1));
				sat.Or(2*i+0, 2*i+1);
				for (int j = 0; j < i; j++) {
					for (int k = 0; k < 2; k++) {
						for (int l = 0; l < 2; l++) {
							if (cs[i][k][0].equals(cs[j][l][0]) || cs[i][k][1].equals(cs[j][l][1])) {
								sat.Or(sat.Not(2*i+k), sat.Not(2*j+l));
//								dump(i, j, k, l);
							}
						}
					}
				}
			}
			if (!sat.satisfy()) {
				io.out.println("Impossible");
				return;
			}
			for (int i = 0; i < n; i++) {
				swap(cs[i][1], 0, 1);
			}
			for (int i = 0; i < 2*n; i++) {
				if (sat.ans[i]) {
					io.out.println(cs[i/2][i%2][0] + " " + cs[i/2][i%2][1]);
				}
			}
		}
	}
	
	int toNum(char c) {
		if (Character.isLowerCase(c)) return c - 'a';
		return c - 'A' + 26;
	}
	
	static
	public class Sat2 {
		final int n;
		final boolean[] ans;
		final StronglyConnectedComponent scc;

		void clear() {
			scc.clear();
		}

		public Sat2(int n) {
			this.n = n;
			ans = new boolean[n];
			scc = new StronglyConnectedComponent(n * 2);
		}

		private int Not(int a) {
			if(a < 0 || a >= 2 * n) throw new RuntimeException();
			return a >= n ? a - n : a + n;
		}

		public void Or(int a, int b) {
			if(a < 0 || a >= 2 * n || b < 0 || b >= 2 * n) throw new RuntimeException();
			scc.addEdge(Not(a), b);
			scc.addEdge(Not(b), a);
		}

		public boolean satisfy() {
			scc.scc();
			for(int i = 0; i < n; i++) {
				// 同じ強連結成分に含まれたら充足不可能
				if(scc.cmp[i] == scc.cmp[i + n]) {
					return false;
				}
			}

			for(int i = 0; i < n; i++) {
				ans[i] = scc.cmp[i] > scc.cmp[i + n];
			}

			return true;
		}

		static public class StronglyConnectedComponent {
			int V;
			List<List<Integer>> G;
			List<List<Integer>> rG;
			List<Integer> vs;
			boolean[] used;
			public int[] cmp;

			void clear() {
				for (int i = 0; i < V; i++) {
					G.get(i).clear();
					rG.get(i).clear();
				}
			}

			public StronglyConnectedComponent(int n) {
				V = n;
				G = new ArrayList<List<Integer>>(n);
				rG = new ArrayList<List<Integer>>(n);
				vs = new ArrayList<Integer>();
				used = new boolean[n];
				cmp = new int[n];
				for (int i = 0; i < n; i++) {
					G.add(new ArrayList<Integer>());
					rG.add(new ArrayList<Integer>());
				}
			}

			public void addEdge(int from, int to) {
				G.get(from).add(to);
				rG.get(to).add(from);
			}

			private void dfs(int v) {
				used[v] = true;
				for (int i = 0; i < G.get(v).size(); i++)
					if (!used[G.get(v).get(i)])
						dfs(G.get(v).get(i));
				vs.add(v);
			}

			private void rdfs(int v, int k) {
				used[v] = true;
				cmp[v] = k;
				for (int i = 0; i < rG.get(v).size(); i++)
					if (!used[rG.get(v).get(i)])
						rdfs(rG.get(v).get(i), k);
			}

			public int scc() {
				for (int i = 0; i < V; i++)
					used[i] = false;
				vs.clear();
				for (int i = 0; i < V; i++)
					if (!used[i])
						dfs(i);
				for (int i = 0; i < V; i++)
					used[i] = false;
				int k = 0;
				for (int i = vs.size() - 1; i >= 0; i--)
					if (!used[vs.get(i)])
						rdfs(vs.get(i), k++);
				return k;
			}

		}
	}
	
	/// TEMPLATE
	static int gcd(int n, int r) { return r == 0 ? n : gcd(r, n%r); }
	static long gcd(long n, long r) { return r == 0 ? n : gcd(r, n%r); }
	
	static <T> void swap(T[] x, int i, int j) { T t = x[i]; x[i] = x[j]; x[j] = t; }
	static void swap(int[] x, int i, int j) { int t = x[i]; x[i] = x[j]; x[j] = t; }

	void printArrayLn(int[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); }
	void printArrayLn(long[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); }
	
	static void dump(Object... o) { System.err.println(Arrays.deepToString(o)); } 
	
	void main() throws IOException {
		//		IOFast.setFileIO("rle-size.in", "rle-size.out");
		try { run(); }
		catch (EndOfFileRuntimeException e) { }
		io.out.flush();
	}
	public static void main(String[] args) throws IOException { new _470().main(); }
	
	static class EndOfFileRuntimeException extends RuntimeException {
		private static final long serialVersionUID = -8565341110209207657L; }

	static
	public class IOFast {
		private InputStream in = System.in;
		private PrintWriter out = new PrintWriter(System.out);

		private static int pos, readLen;
		private static final byte[] buffer = new byte[1024 * 8];
		private static char[] str = new char[500*8*2];
		private static boolean[] isDigit = new boolean[256];
		private static boolean[] isSpace = new boolean[256];
		private static boolean[] isLineSep = new boolean[256];

		static { for(int i = 0; i < 10; i++) { isDigit['0' + i] = true; } isDigit['-'] = true; isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true; isLineSep['\r'] = isLineSep['\n'] = true; }
		public byte read() throws IOException { if(pos >= readLen) { pos = 0; readLen = in.read(buffer); if(readLen <= 0) { throw new EndOfFileRuntimeException(); } } return buffer[pos++]; }
		public int nextInt() throws IOException {
			byte first = (byte)nextChar();
			boolean minus = false;
			int res = 0;
			if (first == '-') {
				minus = true;
			} else {
				res = first - '0';
			}
			while (true) {
				byte b = read();
				if (isSpace[b]) break;
				res = res * 10 + b - '0';
			}
			return minus ? -res : res;
		}
		public long nextLong() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; long ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; }
		public char nextChar() throws IOException { while(true) { final int c = read(); if(!isSpace[c]) { return (char)c; } } }
		int reads(int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } if(str.length == len) { char[] rep = new char[str.length * 3 / 2]; System.arraycopy(str, 0, rep, 0, str.length); str = rep; } str[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; }
		int reads(char[] cs, int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } cs[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; }
		public char[] nextLine() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isLineSep); try { if(str[len-1] == '\r') { len--; read(); } } catch(EndOfFileRuntimeException e) { ; } return Arrays.copyOf(str, len); }
		public String nextString() throws IOException { return new String(next()); }
		public char[] next() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); return Arrays.copyOf(str, len); }
//		public int next(char[] cs) throws IOException { int len = 0; cs[len++] = nextChar(); len = reads(cs, len, isSpace); return len; }
//		public double nextDouble() throws IOException { return Double.parseDouble(nextString()); }
		public double nextDouble() throws IOException {
			double res = nextChar() - '0';
			while (true) {
				byte c = read();
				if (isSpace[c]) return res;
				if (c == '.') break;
				res = res * 10 + c - '0';
			}
			double d = 1;
			while (true) {
				byte c = read();
//				dump(c);
				if (!isDigit[c]) break;
				res = res * 10 + c - '0';
				d *= 10;
			}
//			dump(1);
			return res / d;
		}
		public long[] nextLongArray(final int n) throws IOException { final long[] res = new long[n]; for(int i = 0; i < n; i++) { res[i] = nextLong(); } return res; }
		public int[] nextIntArray(final int n) throws IOException { final int[] res = new int[n]; for(int i = 0; i < n; i++) { res[i] = nextInt(); } return res; }
		public int[][] nextIntArray2D(final int n, final int k) throws IOException { final int[][] res = new int[n][]; for(int i = 0; i < n; i++) { res[i] = nextIntArray(k); } return res; }
		public int[][] nextIntArray2DWithIndex(final int n, final int k) throws IOException { final int[][] res = new int[n][k+1]; for(int i = 0; i < n; i++) { for(int j = 0; j < k; j++) { res[i][j] = nextInt(); } res[i][k] = i; } return res; }
		public double[] nextDoubleArray(final int n) throws IOException { final double[] res = new double[n]; for(int i = 0; i < n; i++) { res[i] = nextDouble(); } return res; }
	}
}