#include <stdlib.h>
#include <stdio.h>

using namespace std;

FILE * input = fopen( "letters.in" , "r");
FILE * output = fopen( "letters.out" , "w");

int main(){
    int N , K;
    fscanf( input , "%d %d" , &N , &K );
    int word[27];
    int result[27];
    
    for ( int i = 0 ; i < 27 ; i++ ){
        word[i] = 0;
        result[i] = 0;    
    }
    
    
     // printf( "%d %d\n" , N , K );
    
    char c;
    int read = 0;
    while( true ){
       fscanf( input, "%c" , &c );
       if ( c < 97 || c > 122) continue; 
       word[c - 'a'] ++;
       read ++;
       if( read == N ) break;       
    }
    
    
    int used = 0;    
    for ( int i = 0; i < 26 ;i++ ){
        if ( used >= K ) break;
        if ( word[i] > 0 ) {
           result[i]++;
           word[i]--;
           used++;
        }
    }   
    
    int add;
    for ( int i = 0 ; i < 26 ; i++ ){
        if ( used >= K ) break;
        
        add = 0;
        if ( word[i] > 0 ){
           if ( used + word[i] > K  ){ add = K - used ; }
           else { add = word[i]; }
           
           
           result[i]+=add;
           word[i]-=add;
           used+=add;
        }
    }
    
    
    for ( int i = 0; i < 26 ; i++ ){
        if( result[i] == 0 ) continue;
        
        for( int j = 0; j < result[i] ;j++ ){
             fprintf( output, "%c" , i + 'a' );     
        }
    }
    fprintf( output, "\n" );
    
    return 0;    
}