Problem: Bertown has n junctions and m bidirectional roads. We know that one can get from any junction to any other one by the existing roads. 

As there were more and more cars in the city, traffic jams started to pose real problems. To deal with them the government decided to make the traffic one-directional on all the roads, thus easing down the traffic. Your task is to determine whether there is a way to make the traffic one-directional so that there still is the possibility to get from any junction to any other one. If the answer is positive, you should also find one of the possible ways to orient the roads.

Input

The first line contains two space-separated integers n and m (2 ≤ n ≤ 105, n - 1 ≤ m ≤ 3·105) which represent the number of junctions and the roads in the town correspondingly. Then follow m lines, each containing two numbers which describe the roads in the city. Each road is determined by two integers ai and bi (1 ≤ ai, bi ≤ n, ai ≠ bi) — the numbers of junctions it connects.

It is guaranteed that one can get from any junction to any other one along the existing bidirectional roads. Each road connects different junctions, there is no more than one road between each pair of junctions.

Output

If there's no solution, print the single number 0. Otherwise, print m lines each containing two integers pi and qi — each road's orientation. That is the traffic flow will move along a one-directional road from junction pi to junction qi. You can print the roads in any order. If there are several solutions to that problem, print any of them.

Examples

Input

6 8
1 2
2 3
1 3
4 5
4 6
5 6
2 4
3 5


Output

1 2
2 3
3 1
4 5
5 6
6 4
4 2
3 5


Input

6 7
1 2
2 3
1 3
4 5
4 6
5 6
2 4


Output

0

Solution (in JAVA):

Solution:
import java.io.*;
import java.util.*;
import static java.lang.Math.*;
import static java.util.Arrays.fill;
import static java.util.Arrays.binarySearch;
import static java.util.Arrays.sort;

public class Main {
	public static void main(String[] args) throws IOException {
		new Thread(null, new Runnable() {
			public void run() {
				try {
					try {
						if (new File("input.txt").exists())
							System.setIn(new FileInputStream("input.txt"));
					} catch (SecurityException e) {}
					
					long prevTime = System.currentTimeMillis();
					new Main().run();
					System.err.println("Total time: " + (System.currentTimeMillis() - prevTime) + " ms");
					System.err.println("Memory status: " + memoryStatus());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}, "1", 1L << 24).start(); 
	}

	void run() throws IOException {
		in = new BufferedReader(new InputStreamReader(System.in));
		out = new PrintWriter(System.out);
		solve();
		out.close();
		in.close();
	}
	
	/*************************************************************** 
	 * Solution
	 **************************************************************/
	
	int vNum;
	int eNum;
	MultiList g;
	
	int[] a;
	int[] b;
	boolean[] d;
	
	int[] tin;
	int[] fup;
	boolean[] used;
	
	int time = 0;
	
	void solve() throws IOException  {
		vNum = nextInt();
		eNum = nextInt();
		g = new MultiList(vNum, eNum * 2);
		a = new int [eNum];
		b = new int [eNum];
		d = new boolean [eNum];
		for (int i = 0; i < eNum; i++) {
			int u = nextInt() - 1;
			int v = nextInt() - 1;
			g.add(u, v, i);
			g.add(v, u, -(i + 1));
			a[i] = u + 1;
			b[i] = v + 1;
		}
		
		used = new boolean [vNum];
		tin = new int [vNum];
		fup = new int [vNum];
		
		try {
			for (int v = 0; v < vNum; v++) {
				dfsBridge(v, -1);
			}
		} catch (BridgeFoundException e) {
			out.println(0);
			return;
		}
		
		fill(used, false);
		dfs(0);
		for (int v = 0; v < vNum; v++)
			if (!used[v]) {
				out.println(0);
				return;
			}
		for (int i = 0; i < eNum; i++) {
			if (d[i]) {
				out.println(a[i] + " " + b[i]);
			} else {
				out.println(b[i] + " " + a[i]);
			}
		}
	}
	
	void dfsBridge(int v, int p) throws BridgeFoundException {
		used[v] = true;
		tin[v] = fup[v] = time++;
		
		for (int i = g.head[v]; i != 0; i = g.next[i]) {
			int nv = g.vert[i];
			if (nv == p) continue;
			if (used[nv]) {
				fup[v] = min(fup[v], tin[nv]);
			} else {
				dfsBridge(nv, v);
				fup[v] = min(fup[v], fup[nv]);
				if (tin[v] < fup[nv])
					throw new BridgeFoundException();
			}
		}
	}

	void dfs(int v) {
		used[v] = true;
		for (int i = g.head[v]; i != 0; i = g.next[i]) {
			int nv = g.vert[i];
			int e = g.edge[i];
			int re = e < 0 ? -(e + 1) : e;
			d[re] = e >= 0;
			if (!used[nv])
				dfs(nv);
		}
	}

	class MultiList {
		int[] head;
		int[] next;
		int[] vert;
		int[] edge;
		int cnt = 1;
		
		MultiList(int vNum, int eNum) {
			head = new int [vNum];
			next = new int [eNum + 1];
			vert = new int [eNum + 1];
			edge = new int [eNum + 1];
		}
		
		void add(int u, int v, int e) {
			next[cnt] = head[u];
			vert[cnt] = v;
			edge[cnt] = e;
			head[u] = cnt++;
		}
	}
	
	class BridgeFoundException extends Exception {
		private static final long serialVersionUID = 250828672568755601L;
	}

	/*************************************************************** 
	 * Input 
	 **************************************************************/
	BufferedReader in;
	PrintWriter out;
	StringTokenizer st = new StringTokenizer("");
	
	String nextToken() throws IOException {
		while (!st.hasMoreTokens())
			st = new StringTokenizer(in.readLine());
		return st.nextToken();
	}
	
	int nextInt() throws IOException {
		return Integer.parseInt(nextToken());
	}
	
	long nextLong() throws IOException {
		return Long.parseLong(nextToken());
	}
	
	double nextDouble() throws IOException {
		return Double.parseDouble(nextToken());
	}
	
	int[] nextIntArray(int size) throws IOException {
		int[] ret = new int [size];
		for (int i = 0; i < size; i++)
			ret[i] = nextInt();
		return ret;
	}
	
	long[] nextLongArray(int size) throws IOException {
		long[] ret = new long [size];
		for (int i = 0; i < size; i++)
			ret[i] = nextLong();
		return ret;
	}
	
	double[] nextDoubleArray(int size) throws IOException {
		double[] ret = new double [size];
		for (int i = 0; i < size; i++)
			ret[i] = nextDouble();
		return ret;
	}
	
	String nextLine() throws IOException {
		st = new StringTokenizer("");
		return in.readLine();
	}
	
	boolean EOF() throws IOException {
		while (!st.hasMoreTokens()) {
			String s = in.readLine();
			if (s == null)
				return true;
			st = new StringTokenizer(s);
		}
		return false;
	}
	
	/*************************************************************** 
	 * Output 
	 **************************************************************/
	void printRepeat(String s, int count) {
		for (int i = 0; i < count; i++)
			out.print(s);
	}
	
	void printArray(int[] array) {
		for (int i = 0; i < array.length; i++) {
			if (i > 0) out.print(' ');
			out.print(array[i]);
		}
		out.println();
	}
	
	void printArray(long[] array) {
		for (int i = 0; i < array.length; i++) {
			if (i > 0) out.print(' ');
			out.print(array[i]);
		}
		out.println();
	}
	
	void printArray(double[] array) {
		for (int i = 0; i < array.length; i++) {
			if (i > 0) out.print(' ');
			out.print(array[i]);
		}
		out.println();
	}
	
	void printArray(double[] array, String spec) {
		for (int i = 0; i < array.length; i++) {
			if (i > 0) out.print(' ');
			out.printf(Locale.US, spec, array[i]);
		}
		out.println();
	}
	
	void printArray(Object[] array) {
		boolean blank = false;
		for (Object x : array) {
			if (blank) out.print(' '); else blank = true;
			out.print(x);
		}
		out.println();
	}
	
	@SuppressWarnings("rawtypes")
	void printCollection(Collection collection) {
		boolean blank = false;
		for (Object x : collection) {
			if (blank) out.print(' '); else blank = true;
			out.print(x);
		}
		out.println();
	}
	
	/*************************************************************** 
	 * Utility
	 **************************************************************/
	static String memoryStatus() {
		return (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory() >> 20) + "/" + (Runtime.getRuntime().totalMemory() >> 20) + " MB";
	}
	
	static void checkMemory() {
		System.err.println(memoryStatus());
	}
	
	static long prevTimeStamp = Long.MIN_VALUE;
	
	static void updateTimer() {
		prevTimeStamp = System.currentTimeMillis();
	}
	
	static long elapsedTime() {
		return (System.currentTimeMillis() - prevTimeStamp);
	}
	
	static void checkTimer() {
		System.err.println(elapsedTime() + " ms");
	}
}