Calculate the minimum number of characters you need to change in the string s, so that it contains at least k different letters, or print that it is impossible.

String s consists only of lowercase Latin letters, and it is allowed to change characters only to lowercase Latin letters too.

Input

First line of input contains string s, consisting only of lowercase Latin letters (1 ≤ |s| ≤ 1000, |s| denotes the length of s).

Second line of input contains integer k (1 ≤ k ≤ 26).

Output

Print single line with a minimum number of necessary changes, or the word «impossible» (without quotes) if it is impossible.

Examples

Input

yandex
6


Output

0


Input

yahoo
5


Output

1


Input

google
7


Output

impossible

Note

In the first test case string contains 6 different letters, so we don't need to change anything.

In the second test case string contains 4 different letters: {'a', 'h', 'o', 'y'}. To get 5 different letters it is necessary to change one occurrence of 'o' to some letter, which doesn't occur in the string, for example, {'b'}.

In the third test case, it is impossible to make 7 different letters because the length of the string is 6.
import java.util.*;
import java.io.*;

/**
 * 24-Aug-2017
 * 10:05:22 PM
 * @author HulkBuster
 * 
 */
public class CF844A {
public static int mod = (int) (1e9 + 7);
public static InputReader in;
public static PrintWriter out;

public static void solve() throws FileNotFoundException {

	in = new InputReader(System.in);
	out = new PrintWriter(System.out);
	String s = in.nextLine();
	int k = in.ni();
	
	int l = s.length();
	char ar[] = s.toCharArray();
	if(k>l)
		out.println("impossible");
	else{
		HashSet<Character>hs = new HashSet<>();
		for(int i=0;i<l;i++)
			hs.add(ar[i]);
		int x = hs.size();
		out.print(Math.max(0, k-x));
	}
	out.close();
}

public static void main(String[] args) {
	new Thread(null, new Runnable() {
		public void run() {
			try {
				solve();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}, "1", 1 << 26).start();
}

static class Pair implements Comparable<Pair> {

	int x, y, i;

	Pair(int x, int y, int i) {
		this.x = x;
		this.y = y;
		this.i = i;
	}

	Pair(int x, int y) {
		this.x = x;
		this.y = y;
	}

	public int compareTo(Pair o) {
		if (this.x != o.x)
			return Integer.compare(this.x, o.x);
		else
			return Integer.compare(this.y, o.y);
		//return 0;
	}

	public boolean equals(Object o) {
		if (o instanceof Pair) {
			Pair p = (Pair) o;
			return p.x == x && p.y == y && p.i == i;
		}
		return false;
	}

	public int hashCode() {
		return new Integer(x).hashCode() * 31 + new Integer(y).hashCode() + new Integer(i).hashCode() * 37;
	}

}

public static long add(long a, long b) {
	long x = (a + b);
	while (x >= mod)
		x -= mod;
	return x;
}

public static long sub(long a, long b) {
	long x = (a - b);
	while (x < 0)
		x += mod;
	return x;
}

public static long mul(long a, long b) {
	long x = (a * b);
	while (x >= mod)
		x -= mod;
	return x;
}

public static boolean isPal(String s) {
	for (int i = 0, j = s.length() - 1; i <= j; i++, j--) {
		if (s.charAt(i) != s.charAt(j))
			return false;
	}
	return true;
}

public static String rev(String s) {
	StringBuilder sb = new StringBuilder(s);
	sb.reverse();
	return sb.toString();
}

public static long gcd(long x, long y) {
	if (x % y == 0)
		return y;
	else
		return gcd(y, x % y);
}

public static int gcd(int x, int y) {
	if (x % y == 0)
		return y;
	else
		return gcd(y, x % y);
}

public static long gcdExtended(long a, long b, long[] x) {

	if (a == 0) {
		x[0] = 0;
		x[1] = 1;
		return b;
	}
	long[] y = new long[2];
	long gcd = gcdExtended(b % a, a, y);

	x[0] = y[1] - (b / a) * y[0];
	x[1] = y[0];

	return gcd;
}

public static long mulmod(long a, long b, long m) {
	if (m <= 1000000009)
		return a * b % m;

	long res = 0;
	while (a > 0) {
		if ((a & 1) != 0) {
			res += b;
			if (res >= m)
				res -= m;
		}
		a >>= 1;
		b <<= 1;
		if (b >= m)
			b -= m;
	}
	return res;
}

public static int abs(int a, int b) {
	return (int) Math.abs(a - b);
}

public static long abs(long a, long b) {
	return (long) Math.abs(a - b);
}

public static int max(int a, int b) {
	if (a > b)
		return a;
	else
		return b;
}

public static int min(int a, int b) {
	if (a > b)
		return b;
	else
		return a;
}

public static long max(long a, long b) {
	if (a > b)
		return a;
	else
		return b;
}

public static long min(long a, long b) {
	if (a > b)
		return b;
	else
		return a;
}

public static long pow(long n, long p, long m) {
	long result = 1;
	if (p == 0)
		return 1;
	if (p == 1)
		return n;
	while (p != 0) {
		if (p % 2 == 1)
			result *= n;
		if (result >= m)
			result %= m;
		p >>= 1;
		n *= n;
		if (n >= m)
			n %= m;
	}
	return result;
}

public static long pow(long n, long p) {
	long result = 1;
	if (p == 0)
		return 1;
	if (p == 1)
		return n;
	while (p != 0) {
		if (p % 2 == 1)
			result *= n;
		p >>= 1;
		n *= n;
	}
	return result;
}

public static void debug(Object... o) {
	System.out.println(Arrays.deepToString(o));
}

static class InputReader {
	private final InputStream stream;
	private final byte[] buf = new byte[8192];
	private int curChar, snumChars;
	private SpaceCharFilter filter;

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

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

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

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

	public int[] nIArr(int n) {
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = ni();
		}
		return a;
	}

	public long[] nLArr(int n) {
		long a[] = new long[n];
		for (int i = 0; i < n; i++) {
			a[i] = nl();
		}
		return a;
	}

	public String readString() {
		int c = snext();
		while (isSpaceChar(c)) {
			c = snext();
		}
		StringBuilder res = new StringBuilder();
		do {
			res.appendCodePoint(c);
			c = snext();
		} while (!isSpaceChar(c));
		return res.toString();
	}

	public String nextLine() {
		int c = snext();
		while (isSpaceChar(c))
			c = snext();
		StringBuilder res = new StringBuilder();
		do {
			res.appendCodePoint(c);
			c = snext();
		} while (!isEndOfLine(c));
		return res.toString();
	}

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

	private boolean isEndOfLine(int c) {
		return c == '\n' || c == '\r' || c == -1;
	}

	public interface SpaceCharFilter {
		public boolean isSpaceChar(int ch);
	}

}
}
