#include <bits/stdc++.h>   using namespace std;   int main(int argc, char* argv[]) {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int k;     string str;     cin >> str;     cin >> k;     int temp[50];     memset(temp, 0, sizeof(temp));     int count = 0;     for (int i = 0; i < str.size(); ++i) {       if (temp[(int)(str[i] -  a )] == 0) {         count++;         temp[str[i] -  a ] = 1;       }     }     if (count >= k) {       cout <<  0  << endl;     } else if (k > (int)str.size()) {       cout <<  impossible  << endl;     } else {       cout << k - count << endl;     }     return 0;   }   