How to Repaint a Fence

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Read problems statements in Mandarin Chinese and Russian as well.
John's barn has a fence consisting of N consecutive parts numbered from left to right starting from 1 to N. Each part is initially painted in one of two colors: red or green, whose information is provided you by a string C. The color of ith part C_{i} will be equal to 'R' if the color of the part is red and 'G' if it is green.
John decided to paint the whole fence in green color. To make the mundane process of painting more entertaining he decided to do it using the following process. Every minute (until the whole fence is painted green) he will do the following steps:
 Choose any part of the fence that is painted red. Let's denote the index of this part as X.
 For each part with indices X, X+1, ..., min(N, X + K  1), flip the color of the corresponding part from red to green and from green to red by repainting.
John is wondering how fast he can repaint the fence. Please help him in finding the minimum number of minutes required in repainting.
Input
The first line of the input contains an integer T denoting the number of test cases. The description of T test cases follows.
The first line of each test case contains the two integers N and K.
The next line contains the string C.
Output
For each test case, output a single line containing the answer to the corresponding test case.
Constraints
 1 ≤ T ≤ 10
 1 ≤ N, K ≤ 10^{5}
 C will consist only of uppercase English characters 'R' and 'G'.
Example
Input: 1 7 3 RGGRGRG Output: 4
Explanation
Example case 1. One optimal solution (with 4 steps) looks like this:
 Choose the 1st character (1based index) and get "GRRRGRG".
 Choose the 2st character (1based index) and get "GGGGGRG".
 Choose the 6th character (1based index) and get "GGGGGGR".
 Choose the 7th charatcer (1based index) and get "GGGGGGG".
 Now repainting is done :) It took total 4 steps. Hence answer is 4.
Author:  witua 
Tester:  iscsi 
Editorial  http://discuss.codechef.com/problems/STRBIT 
Tags  bit, cook56, easy, segmenttree, witua 
Date Added:  19032015 
Time Limit:  1 sec 
Source Limit:  50000 Bytes 
Languages:  C, CPP14, JAVA, PYTH, PYTH 3.5, PYPY, CS2, PAS fpc, PAS gpc, RUBY, PHP, GO, NODEJS, HASK, SCALA, D, PERL, FORT, WSPC, ADA, CAML, ICK, BF, ASM, CLPS, PRLG, ICON, SCM qobi, PIKE, ST, NICE, LUA, BASH, NEM, LISP sbcl, LISP clisp, SCM guile, JS, ERL, TCL, PERL6, TEXT, SCM chicken, CLOJ, FS 
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