Problem: Xenny was a teacher and his class consisted of N boys and N girls. He took all his students to the playground and asked them to stand in a straight line. The boys and the girls formed a perfect line, but Xenny seemed unhappy. He wanted them to form an alternating sequence of boys and girls, i.e., he wanted that after a boy, there should be a girl in the line, and vice-versa.

In order to form an alternating sequence, a boy and a girl could swap their positions.

Given the original sequence in which the boys and girls were standing, find the minimum number of swaps required to form an alternating sequence.

Note: An alternating sequence can start either with a boy or a girl.

Input
First line of input consists of a natural number T - the number of testcases.
T testcases follow. For each testcase:

First line consists of a single integer N - the number of boys, and the number of girls.
Second line consists of a string of length 2N, representing the original sequence.
In this string, a boy is represented by uppercase character B and a girl by G.

Output
For each testcase, print the minimum number of swaps required to get an alternating sequence on a new line.

Constraints
1 ≤ T ≤ 5

1 ≤ N ≤ 10^6

SAMPLE INPUT
1
2
BBGG

SAMPLE OUTPUT
1

Explanation

The first boy from left  can swap his position with the first girl from right to get the sequence:

GBGB

This is an alternating sequence and it was obtained using 1 swap.

Solution (in PYTHON):

Solution:
'''
# Read input from stdin and provide input before running code

name = raw_input('What is your name?\n')
print 'Hi, %s.' % name
'''
test = int(raw_input())

boys = [0]*test
text = [None]*test 

for i in range(test):
	boys[i] = int(raw_input())
	text[i] = raw_input()



for i in range(test):
	
	misplacedGinBG = misplacedBinBG = misplacedBinGB = misplacedGinGB = 0
	for index, c in enumerate(text[i]):
		if ((index+1)%2==1):
			if (c== 'G'):
				misplacedGinBG = misplacedGinBG+1
			else:
				misplacedBinGB = misplacedBinGB+1
				
		else:
			if (c == 'B'):
				misplacedBinBG = misplacedBinBG+1
			else:
				misplacedGinGB = misplacedGinGB+1
			
	print min(misplacedGinBG, misplacedBinBG, misplacedBinGB, misplacedGinGB)