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.lang.reflect.Array;
    import java.util.Scanner;
    import java.io.*;
    import java.util.*;
    import java.math.*;
    import java.lang.*;
    import static java.lang.Math.*;
    public class main implements Runnable {

        static ArrayList<Integer> adj[];

        static void Check2(int n) {
            adj = new ArrayList[n + 1];
            for (int i = 0; i <= n; i++) {
                adj[i] = new ArrayList<>();
            }

        }
        static void add(int i, int j) {
            adj[i].add(j);
            adj[j].add(i);
        }


        public static void main(String[] args) {
            new Thread(null, new main(), "Check2", 1 << 26).start();// to increse stack size in java
        }
        static long mod = (long) (1e9 + 7);
        public void run() {
            InputReader in = new InputReader(System.in);
            PrintWriter w = new PrintWriter(System.out);


            char c[]=in.next().toCharArray();
            int f[]=new int[26];
            int k=in.nextInt();

            for(int i=0;i<c.length;i++)f[c[i]-97]++;

            int co=0;
            for(int i=0;i<26;i++){

                if(f[i]!=0)
                co++;

            }
            if(k>c.length)w.println("impossible");
            else if(co>=k)w.println(0);
            else{

                w.println(k-co);

            }






            w.close();
        }
        static class cmp implements Comparator<pair>{

            public int compare(pair o1,pair o2){
                return o1.dist-o2.dist;
            }

        }
        static class pair {
            int val,dist;
            pair(int a,int b){
                val=a;
                dist=b;
            }

        }

        static long modinv(long a,long b)
        {
            long p=power(b,mod-2);

            p=a%mod*p%mod;
            p%=mod;

            return p;

        }

        static long power(long x,long y){
            if(y==0)return 1%mod;
            if(y==1)return x%mod;


            long res=1;
            x=x%mod;
            while(y>0){


                if((y%2)!=0){
                    res=(res*x)%mod;
                }


                y=y/2;
                x=(x*x)%mod;
            }


            return res;

        }
        static  int gcd(int a,int b){

            if(b==0)return a;
            return gcd(b,a%b);
        }

        static  void sev(int a[],int n){

            for(int i=2;i<=n;i++)a[i]=i;
            for(int i=2;i<=n;i++){

                if(a[i]!=0){
                    for(int j=2*i;j<=n;){

                        a[j]=0;
                        j=j+i;
                    }
                }

            }

        }



        static class node{

            int y;
            int val;

            node(int a,int b){

                y=a;
                val=b;

            }


        }

        static class InputReader
        {
            private InputStream stream;
            private byte[] buf = new byte[1024];
            private int curChar;
            private int numChars;
            private SpaceCharFilter filter;

            public InputReader(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 String nextLine()
            {
                BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
                String str = "";
                try
                {
                    str = br.readLine();
                }
                catch (IOException e)
                {
                    e.printStackTrace();
                }
                return str;
            }
            public int nextInt()
            {
                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 nextLong()
            {
                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 double nextDouble()
            {
                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, nextInt());
                    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, nextInt());
                        if (c < '0' || c > '9')
                            throw new InputMismatchException();
                        m /= 10;
                        res += (c - '0') * m;
                        c = read();
                    }
                }
                return res * sgn;
            }

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

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

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







    }