Problem: Little Susie loves strings. Today she calculates distances between them. As Susie is a small girl after all, her strings contain only digits zero and one. She uses the definition of Hamming distance:

We will define the distance between two strings s and t of the same length consisting of digits zero and one as the number of positions i, such that si isn't equal to ti. 

As besides everything else Susie loves symmetry, she wants to find for two strings s and t of length n such string p of length n, that the distance from p to s was equal to the distance from p to t.

It's time for Susie to go to bed, help her find such string p or state that it is impossible.

Input

The first line contains string s of length n. 

The second line contains string t of length n.

The length of string n is within range from 1 to 105. It is guaranteed that both strings contain only digits zero and one.

Output

Print a string of length n, consisting of digits zero and one, that meets the problem statement. If no such string exist, print on a single line "impossible" (without the quotes).

If there are multiple possible answers, print any of them.

Examples

Input

0001
1011


Output

0011


Input

000
111


Output

impossible

Note

In the first sample different answers are possible, namely — 0010, 0011, 0110, 0111, 1000, 1001, 1100, 1101.

Solution (in JAVA):

Solution:
//################################################################################################################
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import java.math.BigInteger;
import java.util.InputMismatchException;

//################################################################################################################
public class R303D2B {
	public static void main(String[] args) {
		R303D2B b = new R303D2B();
		InputReader1 reader = b.new InputReader1(System.in);
		OutputWriter writer = b.new OutputWriter(System.out);
		// think about the brute-force approach
		// read input
		// code boundary conditions
		String s = reader.readLine();
		String t = reader.readLine();
		int psd = 0;
		int ptd = 0;
		StringBuilder p = new StringBuilder();
		int diff = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.charAt(i) != t.charAt(i)) {
				diff++;
			}
		}
		if (diff % 2 != 0) {
			writer.println("impossible");
		} else {
			if (diff == 0) {
				writer.println(s);
			} else {
				for (int i = 0; i < s.length(); i++) {
					char si = s.charAt(i);
					char ti = t.charAt(i);
					if (si != ti) {
						if (psd >= ptd) {
							p.append(si);
							ptd++;
						} else {
							p.append(ti);
							psd++;
						}
					} else {
						p.append(si);
					}
				}
				writer.println(p.toString());
			}
		}
		reader.close();
		writer.close();
	}

	class InputReader1 {
		// private final boolean finished = false;

		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;

		public InputReader1(InputStream stream) {
			this.stream = stream;
		}

		public int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		public int peek() {
			if (numChars == -1)
				return -1;
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					return -1;
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar];
		}

		public int readInt() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}

		public long readLong() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}

		public String readString() {
			int length = readInt();
			if (length < 0)
				return null;
			byte[] bytes = new byte[length];
			for (int i = 0; i < length; i++)
				bytes[i] = (byte) read();
			try {
				return new String(bytes, "UTF-8");
			} catch (UnsupportedEncodingException e) {
				return new String(bytes);
			}
		}

		public boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		private String readLine0() {
			StringBuffer buf = new StringBuffer();
			int c = read();
			while (c != '\n' && c != -1) {
				if (c != '\r')
					buf.appendCodePoint(c);
				c = read();
			}
			return buf.toString();
		}

		public String readLine() {
			String s = readLine0();
			while (s.trim().length() == 0)
				s = readLine0();
			return s;
		}

		public String readLine(boolean ignoreEmptyLines) {
			if (ignoreEmptyLines)
				return readLine();
			else
				return readLine0();
		}

		public BigInteger readBigInteger() {
			try {
				return new BigInteger(readString());
			} catch (NumberFormatException e) {
				throw new InputMismatchException();
			}
		}

		public char readCharacter() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			return (char) c;
		}

		public double readDouble() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			double res = 0;
			while (!isSpaceChar(c) && c != '.') {
				if (c == 'e' || c == 'E')
					return res * Math.pow(10, readInt());
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			}
			if (c == '.') {
				c = read();
				double m = 1;
				while (!isSpaceChar(c)) {
					if (c == 'e' || c == 'E')
						return res * Math.pow(10, readInt());
					if (c < '0' || c > '9')
						throw new InputMismatchException();
					m /= 10;
					res += (c - '0') * m;
					c = read();
				}
			}
			return res * sgn;
		}

		public boolean isExhausted() {
			int value;
			while (isSpaceChar(value = peek()) && value != -1)
				read();
			return value == -1;
		}

		public String next() {
			return readString();
		}

		public boolean readBoolean() {
			return readInt() == 1;
		}

		public void close() {
			try {
				stream.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	class OutputWriter {
		private final PrintWriter writer;

		public OutputWriter(OutputStream stream) {
			writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
					stream)));
		}

		public OutputWriter(Writer writer) {
			this.writer = new PrintWriter(writer);
		}

		public void println(String s) {
			writer.println(s);
		}

		public void println(int x) {
			writer.println(x);
		}

		public void print(int x) {
			writer.print(x);
		}

		public void println(long x) {
			writer.println(x);
		}

		public void printSpace() {
			writer.print(" ");
		}

		public void close() {
			writer.close();
		}
	}
}