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.
// AUTHOR : MAYANK SUNAL

import java.io.*;
import java.util.*;
import java.math.*;

public class Main {
	static final Random random = new Random();
	static PrintWriter out = new PrintWriter((System.out));
	static Reader sc = new Reader();

	public static void main(String args[]) throws IOException {
//		int t = sc.nextInt();
//		while (t-- > 0) {
//        	CODE START FROM HERE long n = sc.nextLong();
		String s = sc.next();
		int k = sc.nextInt();
		if (k > s.length())
			System.out.println("impossible");
		else {
			HashSet<Character> hs = new HashSet<Character>();
			for (char i : s.toCharArray())
				hs.add(i);
			if (hs.size() == k || hs.size() > k)
				System.out.println(0);
			else
				System.out.println(k - hs.size());
		}

//		}

	}

// Fast Input Output
	static class Reader {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer("");

		public String next() {
			while (!st.hasMoreTokens()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

		public String nextLine() {
			try {
				return br.readLine();
			} catch (Exception e) {
				e.printStackTrace();
			}
			return null;
		}

		public boolean hasNext() {
			String next = null;
			try {
				next = br.readLine();
			} catch (Exception e) {
			}
			if (next == null) {
				return false;
			}
			st = new StringTokenizer(next);
			return true;
		}

	}

	// EFFICIENT SORTING Ascending
	static void ruffleSortAsc(Integer[] a) {
		int n = a.length; // shuffle, then sort
		for (int i = 0; i < n; i++) {
			int oi = random.nextInt(n), temp = a[oi];
			a[oi] = a[i];
			a[i] = temp;
		}
		Arrays.sort(a);
	}

//	EFFICIENT SORTING Descending
	static void ruffleSortDesc(Integer[] a) {
		int n = a.length; // shuffle, then sort
		for (int i = 0; i < n; i++) {
			int oi = random.nextInt(n), temp = a[oi];
			a[oi] = a[i];
			a[i] = temp;
		}
		Arrays.sort(a, Collections.reverseOrder());
	}

	// Array Sum
	static long sum(Integer[] arr) {
		long sum = 0;
		for (int i : arr)
			sum += i;
		return sum;
	}

	// ArrayList Sum
	static long sumal(ArrayList<Integer> al) {
		long sum = 0;
		for (int i : al)
			sum += i;
		return sum;
	}

	// swap array elements
	static void swap(int arr1[], int arr2[], int i, int j) {
		int temp = arr1[i];
		arr1[i] = arr2[j];
		arr2[j] = temp;
	}

	// reading array value;
	static void read(Integer[] arr) {
		for (int i = 0; i < arr.length; i++)
			arr[i] = sc.nextInt();
		return;
	}

//    reading arraylistValue

	static void readal(List<Integer> l, int n) {
		for (int i = 0; i < n; i++)
			l.add(sc.nextInt());
		return;
	}

	// check for even odd
	static boolean isEven(long n) {
		return ((n & 1) != 1);
	}

	// max in a array
	static int max(Integer[] arr) {
		int max = Integer.MIN_VALUE;
		for (int i = 0; i < arr.length; i++)
			if (max < arr[i])
				max = arr[i];
		return max;
	}

//  print array
	static void printarr(Integer arr[]) {
		for (int i : arr)
			System.out.println(i);
	}

// ceil of two elements
	static int ceil(int a, int b) {
		return (int) Math.ceil(((double) a / (double) b));
	}

// floor of two elements
	static int floor(int a, int b) {
		return (int) Math.floor(((double) a / (double) b));
	}
}