CF121B.Lucky Transformation
普及/提高-
通过率:0%
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题目描述
Petya loves lucky numbers. Everybody knows that lucky numbers are positive integers whose decimal representation contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.
Petya has a number consisting of n digits without leading zeroes. He represented it as an array of digits without leading zeroes. Let's call it d . The numeration starts with 1 , starting from the most significant digit. Petya wants to perform the following operation k times: find the minimum x (1<=x<n) such that dx=4 and dx+1=7 , if x is odd, then to assign dx=dx+1=4 , otherwise to assign dx=dx+1=7 . Note that if no x was found, then the operation counts as completed and the array doesn't change at all.
You are given the initial number as an array of digits and the number k . Help Petya find the result of completing k operations.
输入格式
The first line contains two integers n and k (1<=n<=105,0<=k<=109) — the number of digits in the number and the number of completed operations. The second line contains n digits without spaces representing the array of digits d , starting with d1 . It is guaranteed that the first digit of the number does not equal zero.
输出格式
In the single line print the result without spaces — the number after the k operations are fulfilled.
输入输出样例
输入#1
7 4 4727447
输出#1
4427477
输入#2
4 2 4478
输出#2
4478
说明/提示
In the first sample the number changes in the following sequence: 4727447→4427447→4427477→4427447→4427477 .
In the second sample: 4478→4778→4478 .