| Erasing and Winning |
Juliano is a fan of the TV show Erasing and Winning, where participants are selected in a draw and receive money for taking part in the show.
In the show, the presenter writes a number of N digits in a board. The participant must then erase exactly D digits from the number in the board; the number formed by the remaining digits is the value of the money prize for the participant.
Juliano was at last selected to take part in the show, and asked you to write a program that, given the number the presenter wrote in the board, and the number of digits Juliano must erase, determines the highest value of the prize he can win.
The input contains several test cases. The first line of a test case contains two integers N and D (1 ≤ D < N ≤ 105) indicating respectively the number of digits of the number the presenter wrote in the board and the number of digits that must be erased. The next line contains the number the presenter wrote; the number does not start with a zero.
The end of input is indicated by a line containing only two zeros, separated by a space.
For each test case in the input your program must produce one single line in the output, containing the highest prize Juliano can win.
4 2 3759 6 3 123123 7 4 1000000 0 0
79 323 100