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
'''
t = int(raw_input())
for qq in xrange(t):
	n = int(raw_input())
	b = raw_input()
	a = [0 for i in xrange(2*n)]
	for i in xrange(2*n):
		if b[i] == 'B':
			a[i] = 1
	s1 = [0 for i in xrange(2*n)]
	s2 = [0 for i in xrange(2*n)]
	for i in xrange(1, 2*n, 2):
		s1[i] = 1
	for i in xrange(0, 2*n, 2):
		s2[i] = 1
	cnt1 = 0
	cnt2 = 0
	for i in xrange(2*n):
		if a[i] != s1[i]:
			cnt1 += 1
		if a[i] != s2[i]:
			cnt2 += 1
	print min(cnt1 // 2, cnt2 // 2)