#include<iostream>
#include <bits/stdc++.h>
 
using namespace std;
 
int main(){
 
  string s;
  cin>>s;
 
  int k;
  cin>>k;
  int mlen=1, len=1;
  string ans = "";
  ans.push_back(s[0]);
  string temp = "";
  temp.push_back(s[0]);
  for(int i=1; i<s.size(); i++){
  	if(abs(s[i]-s[i-1])<=k){
  		len++;
  		temp.push_back(s[i]);
  		if(len>mlen){
  			mlen=len;
  			ans=temp;
  		}
  	}
  	else{
  		len=1;
  		temp="";
  	}
  }
 
  cout<< ans;
  return 0;
}

I2luY2x1ZGU8aW9zdHJlYW0+CiNpbmNsdWRlIDxiaXRzL3N0ZGMrKy5oPgoKdXNpbmcgbmFtZXNwYWNlIHN0ZDsKCmludCBtYWluKCl7CiAgCiAgc3RyaW5nIHM7CiAgY2luPj5zOwogIAogIGludCBrOwogIGNpbj4+azsKICBpbnQgbWxlbj0xLCBsZW49MTsKICBzdHJpbmcgYW5zID0gIiI7CiAgYW5zLnB1c2hfYmFjayhzWzBdKTsKICBzdHJpbmcgdGVtcCA9ICIiOwogIHRlbXAucHVzaF9iYWNrKHNbMF0pOwogIGZvcihpbnQgaT0xOyBpPHMuc2l6ZSgpOyBpKyspewogIAlpZihhYnMoc1tpXS1zW2ktMV0pPD1rKXsKICAJCWxlbisrOwogIAkJdGVtcC5wdXNoX2JhY2soc1tpXSk7CiAgCQlpZihsZW4+bWxlbil7CiAgCQkJbWxlbj1sZW47CiAgCQkJYW5zPXRlbXA7CiAgCQl9CiAgCX0KICAJZWxzZXsKICAJCWxlbj0xOwogIAkJdGVtcD0iIjsKICAJfQogIH0KICAKICBjb3V0PDwgYW5zOwogIHJldHVybiAwOwp9

YWJhYmJhY2EKMQ==

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1