codeforces 844A Diversity

#include<stdio.h>#include<string.h>int main(void){  int k, count, len;  char ch[1005];  while (scanf("%s %d", ch, &k) != EOF) {    count = 0;    if (strlen(ch) < k) {      printf("impossible\n");      continue;    }    for (int i = 0; i < strlen(ch); i++) {      for (int j = i+1; j < strlen(ch); j++) {        if (ch[i] == ch[j]) {          count++;          break;        }      }    }    len = strlen(ch) - count;    if (len >= k) {      printf("0\n");    } else if ((k - len) <= count) {      printf("%d\n", k-len);    } else {      printf("impossible\n");    }  }  return 0;}