import std.stdio, std.array, std.string, std.conv, std.algorithm; import std.typecons, std.range, std.random, std.math, std.container; import std.numeric, std.bigint, core.bitop, core.stdc.stdio; class Kosaraju { int N; int[][] adj; int[][] rev_adj; int[] group; bool[] group_prev; int[][] group_n; this(int n) { N = n; adj = new int[][](N); rev_adj = new int[][](N); group = new int[](N); } void add_edge(int from, int to) { adj[from] ~= to; rev_adj[to] ~= from; } void run() { int[] ord; auto used = new bool[](N); foreach (i; 0..N) if (!used[i]) dfs1(i, ord, used); foreach (i; 0..N) used[i] = false; auto g_num = 0; foreach (i; iota(N-1, -1, -1)) if (!used[ord[i]]) { dfs2(ord[i], g_num, used); g_num += 1; } group_n = new int[][](group.reduce!(max)+1); foreach (i; 0..N) group_n[group[i]] ~= i; group_prev = new bool[](group.reduce!(max)+1); foreach (i; 0..N) foreach (j; adj[i]) if (group[i] != group[j]) group_prev[group[j]] = true; } void dfs1(int from, ref int[] ord, ref bool[] used) { if (used[from]) return; used[from] = true; foreach (to; adj[from]) if (!used[to]) dfs1(to, ord, used); ord ~= from; } void dfs2(int from, int g_num, ref bool[] used) { if (used[from]) return; used[from] = true; group[from] = g_num; foreach (to; rev_adj[from]) if (!used[to]) dfs2(to, g_num, used); } } void main() { auto N = readln.chomp.to!int; auto U = N.iota.map!(_ => readln.chomp).array; if (N > 52) { writeln("Impossible"); return; } auto G = new Kosaraju(2*N); foreach (i; 0..N) { foreach (j; i+1..N) { // (xi => not xj) & (xj => not xi) if (U[i][0] == U[j][0] || U[i][1..3] == U[j][1..3]) G.add_edge(i, j+N), G.add_edge(j, i+N); // (xi => xj) & (not xj => not xi) if (U[i][0] == U[j][2] || U[i][1..3] == U[j][0..2]) G.add_edge(i, j), G.add_edge(j+N, i+N); // (not xi => not xj) & (xj => xi) if (U[i][2] == U[j][0] || U[i][0..2] == U[j][1..3]) G.add_edge(i+N, j+N), G.add_edge(j, i); // (not xi => xj) & (not xj => xi) if (U[i][2] == U[j][2] || U[i][0..2] == U[j][0..2]) G.add_edge(i+N, j), G.add_edge(j+N, i); } } G.run; auto div = new bool[](N); foreach (i; 0..N) { if (G.group[i] == G.group[i+N]) { writeln("Impossible"); return; } else if (G.group[i] > G.group[i+N]) { div[i] = true; } } foreach (i; 0..N) { if (div[i]) writeln(U[i][0], " ", U[i][1..3]); else writeln(U[i][0..2], " ", U[i][2]); } }