public static void main(String[] args) throws IOException {
IO io = new IO(System.in);
int sum;
while (true) {
int nV = io.nextInt();
int nE = io.nextInt();
if (nV == 0) {
break;
}
V[] vertices = new V[nV];
E[] edges = new E[nE];
for (int j = 0; j < nV; j++) {
vertices[j] = new V(j);
}
for (int j = 0; j < nE; j++) {
int start = io.nextInt();
int end = io.nextInt();
double w = io.nextDouble();
if (end > start) {
edges[j] = new E(vertices[start], vertices[end], w);
} else {
edges[j] = new E(vertices[end], vertices[start], w);
}
}
ArrayList<E> result = compute(nV, edges);
if (result.size() > 0) {
sum = 0;
for (int i = 0; i < result.size(); i++) {
sum += result.get(i).w;
}
io.println(sum);
String[] resultStrings = new String[result.size()];
for (int i = 0; i < result.size(); i++) {
resultStrings[i] = "" + result.get(i).start.name + " " + result.get(i).end.name;
}
Arrays.sort(resultStrings);
for (int i = 0; i < result.size(); i++) {
io.printf("%s\n", resultStrings[i]);
}
} else {
io.println("Impossible");
}
}
io.close();
}
