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:
//package round89;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Comparator;
import java.util.Queue;

public class E {
	InputStream is;
	PrintWriter out;
	String INPUT = "";
//	String INPUT = "6 8\r\n" + 
//			"1 2\r\n" + 
//			"2 3\r\n" + 
//			"1 3\r\n" + 
//			"4 5\r\n" + 
//			"4 6\r\n" + 
//			"5 6\r\n" + 
//			"2 4\r\n" + 
//			"3 5";
//	String INPUT = "6 7\r\n" + 
//			"1 2\r\n" + 
//			"2 3\r\n" + 
//			"1 3\r\n" + 
//			"4 5\r\n" + 
//			"4 6\r\n" + 
//			"5 6\r\n" + 
//			"2 4";
	
	void solve()
	{
		int n = ni();
		int m = ni();
		int[] from = new int[m];
		int[] to = new int[m];
		for(int i = 0;i < m;i++){
			from[i] = ni() - 1;
			to[i] = ni() - 1;
		}
		int[][][] g = packWU(n, from, to, new int[m]);
		for(int i = 0;i < g.length;i++){
			if(g[i].length < 2){
				out.println(0);
				return;
			}
			Arrays.sort(g[i], new Comparator<int[]>(){
				public int compare(int[] a, int[] b){
					return a[0] - b[0];
				}
			});
		}
		
		loop = new int[n];
		hist = new int[n];
		findLoop(0, g, -1, 1);
		
		BitSet ved = new BitSet();
		
		for(int i = 0;i < cycle;i++){
			nya.append(loop[i]+1);
			nya.append(' ');
			nya.append(loop[(i+1)%cycle]+1);
			nya.append('\n');
//			out.printf("%d %d\n", loop[i]+1, loop[(i+1)%cycle]+1);
			for(int j = 0;j < g[loop[i]].length;j++){
				if(g[loop[i]][j][0] == loop[(i+1)%cycle]){
					g[loop[i]][j][1] = 1;
				}
				if(g[loop[i]][j][0] == loop[(i+cycle-1)%cycle]){
					g[loop[i]][j][1] = -1;
				}
			}
//			toto[loop[i]] = new int[]{loop[(i+1)%cycle], loop[(i+cycle-1)%cycle]};
			ved.set(loop[i]);
		}
//		tr(loop);
		
		for(int l : loop){
			rec(l, g, -1);
		}
		if(isSource(g, 0, 1) && isSource(g, 0, -1)){
			out.print(nya);
		}else{
			out.println(0);
		}
		
//		int[][] xg = new int[g.length][];
//		for(int i = 0;i < n;i++){
//			xg[i] = new int[g[i].length];
//			int p = 0;
//			for(int j = 0;j < g[i].length;j++){
//				if(g[i][j][1] == 1){
//					xg[i][p++] = g[i][j][0];
//				}
//				if(g[i][j][1] == 0){
//					throw new Error();
//				}
//			}
//			xg[i] = Arrays.copyOf(xg[i], p);
//		}
//		
//		if(isSource(xg, 0) && isSource(invGraph(xg), 0)){
//			out.print(nya);
//		}else{
//			out.println(0);
//		}
	}
	
	static int[][] invGraph(int[][] g)
	{
		int n = g.length;
		int[] p = new int[n];
		for(int f = 0;f < n;f++){
			for(int t : g[f]){
				p[t]++;
			}
		}
		int[][] r = new int[n][];
		for(int i = 0;i < n;i++)r[i] = new int[p[i]];
		for(int f = n-1;f >= 0;f--){
			for(int t : g[f]){
				r[t][--p[t]] = f;
			}
		}
		return r;
	}
	
	public boolean isSource(int[][][] g, int s, int r)
	{
		int n = g.length;
		BitSet ved = new BitSet();
		Queue<Integer> q = new ArrayDeque<Integer>();
		q.add(s);
		ved.set(s);
		while(q.size() > 0){
			int cur = q.poll();
			for(int[] e : g[cur]){
				if(e[1] == r && !ved.get(e[0])){
					ved.set(e[0]);
					q.add(e[0]);
				}
			}
		}
		return ved.cardinality() == n;
	}
	
	public static boolean isSource(int[][] g, int s)
	{
		int n = g.length;
		BitSet ved = new BitSet();
		Queue<Integer> q = new ArrayDeque<Integer>();
		q.add(s);
		ved.set(s);
		while(q.size() > 0){
			int cur = q.poll();
			for(int e : g[cur]){
				if(!ved.get(e)){
					ved.set(e);
					q.add(e);
				}
			}
		}
		return ved.cardinality() == n;
	}
	
	BitSet gved = new BitSet();
	StringBuilder nya = new StringBuilder();
	
	void rec(int pos, int[][][] g, int prev)
	{
		if(gved.get(pos))return;
		gved.set(pos);
		for(int i = 0;i < g[pos].length;i++){
			int[] e = g[pos][i];
			if(e[0] != prev && e[1] == 0){
				g[pos][i][1] = 1;
				int low = 0;
				int high = g[e[0]].length;
				while(high - low > 1){
					int mid = (high + low) / 2;
					if(g[e[0]][mid][0] == pos){
						low = mid;
						break;
					}
					if(g[e[0]][mid][0] < pos){
						low = mid;
					}else{
						high = mid;
					}
				}
				g[e[0]][low][1] = -1;
				nya.append(pos+1);
				nya.append(' ');
				nya.append(e[0]+1);
				nya.append('\n');
				rec(e[0], g, pos);
//				tr(pos, toto[e], e, ret);
			}
		}
	}
	
	int[][] toto;
	int[] loop;
	int cycle;
	int[] hist;
	
	boolean findLoop(int pos, int[][][] g, int prev, int depth)
	{
		if(hist[pos] > 0){
			cycle = depth - hist[pos];
			for(int i = 0;i < g.length;i++){
				if(hist[i] >= hist[pos]){
					loop[hist[i]-hist[pos]] = i;
				}
			}
			loop = Arrays.copyOf(loop, cycle);
			return true;
		}
		
		hist[pos] = depth;
		for(int[] e : g[pos]){
			if(e[0] != prev){
				if(findLoop(e[0], g, pos, depth+1))return true;
			}
		}
		hist[pos] = 0;
		return false;
	}
	
	public static int[][][] packWU(int n, int[] from, int[] to, int[] w)
	{
		int[][][] g = new int[n][][];
		int[] p = new int[n];
		for(int f : from)p[f]++;
		for(int t : to)p[t]++;
		for(int i = 0;i < n;i++)g[i] = new int[p[i]][2];
		for(int i = 0;i < from.length;i++){
			--p[from[i]];
			g[from[i]][p[from[i]]][0] = to[i];
			g[from[i]][p[from[i]]][1] = w[i];
			--p[to[i]];
			g[to[i]][p[to[i]]][0] = from[i];
			g[to[i]][p[to[i]]][1] = w[i];
		}
		return g;
	}
	
	void run() throws Exception
	{
//		int n = 100000;
//		StringBuilder sb = new StringBuilder(n + " " + n*3 + " ");
//		for(int i = 0;i < n;i++){
//			sb.append((i+1) + " " + ((i+1)%n+1) + " ");
//			sb.append((i+1) + " " + ((i+2)%n+1) + " ");
//			sb.append((i+1) + " " + ((i+3)%n+1) + " ");
//		}
//		INPUT = sb.toString();
		
		
		is = oj ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		long s = System.currentTimeMillis();
		solve();
		out.flush();
		tr(System.currentTimeMillis()-s+"ms");
	}
	
	public static void main(String[] args) throws Exception
	{
		new E().run();
	}
	
	public int ni()
	{
		try {
			int num = 0;
			boolean minus = false;
			while((num = is.read()) != -1 && !((num >= '0' && num <= '9') || num == '-'));
			if(num == '-'){
				num = 0;
				minus = true;
			}else{
				num -= '0';
			}
			
			while(true){
				int b = is.read();
				if(b >= '0' && b <= '9'){
					num = num * 10 + (b - '0');
				}else{
					return minus ? -num : num;
				}
			}
		} catch (IOException e) {
		}
		return -1;
	}
	
	public long nl()
	{
		try {
			long num = 0;
			boolean minus = false;
			while((num = is.read()) != -1 && !((num >= '0' && num <= '9') || num == '-'));
			if(num == '-'){
				num = 0;
				minus = true;
			}else{
				num -= '0';
			}
			
			while(true){
				int b = is.read();
				if(b >= '0' && b <= '9'){
					num = num * 10 + (b - '0');
				}else{
					return minus ? -num : num;
				}
			}
		} catch (IOException e) {
		}
		return -1;
	}
	
	public String nline()
	{
		try{
			int b = 0;
			StringBuilder sb = new StringBuilder();
			while((b = is.read()) != -1 && (b == '\r' || b == '\n'));
			if(b == -1)return "";
			sb.append((char)b);
			while(true){
				b = is.read();
				if(b == -1)return sb.toString();
				if(b == '\r' || b == '\n')return sb.toString();
				sb.append((char)b);
			}
		} catch (IOException e) {
		}
		return "";
	}
	
	public String ns()
	{
		try{
			int b = 0;
			StringBuilder sb = new StringBuilder();
			while((b = is.read()) != -1 && (b == '\r' || b == '\n' || b == ' '));
			if(b == -1)return "";
			sb.append((char)b);
			while(true){
				b = is.read();
				if(b == -1)return sb.toString();
				if(b == '\r' || b == '\n' || b == ' ')return sb.toString();
				sb.append((char)b);
			}
		} catch (IOException e) {
		}
		return "";
	}
	
	double nd() { return Double.parseDouble(ns()); }
	boolean oj = System.getProperty("ONLINE_JUDGE") != null;
	void tr(Object... o) { if(!oj)System.out.println(Arrays.deepToString(o)); }
}