#include <bits/stdc++.h>   #pragma GCC optimize( Ofast )   #pragma GCC target( sse,sse2,sse3,sse3,sse4,popcnt,abm,mmx )   using namespace std;   const int MX = 1e9 + 1;   const int Imp = -1;   const int N = 1e6 + 5;   const int M = 1e6 + 5;   const long long INF = 1e18 + 1;   int n, k;   string s;   set<char> st;   int main() {     ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);     string s;     cin >> s;     int k;     cin >> k;     int n = s.size();     if (n < k) {       cout <<  impossible ;     } else {       for (int i = 0; i < n; ++i) st.insert(s[i]);       int x = st.size();       if (x > k)         cout << 0;       else         cout << abs(x - k);     }   }   