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:
import sys

for __ in range(input()) :
    n = input()
    s = list(raw_input())
    seq0 , seq1 = "BG"*n , "GB"*n
    a0 , a1 = 0 , 0
    k = [i for i in s]
    i = 0
    while i < 2*n :
    	j = 1
        if s[i] != seq0[i] :
            j = i+1
            while j < 2*n and seq0[j] == s[j] :
                j += 1
            if j < 2*n :
                s[i] , s[j] = seq0[i] , seq0[j]
            	a0 += 1
            else :
            	break
        i += 1
    s = [i for i in k]
    i = 0
    while i < 2*n :
        j = 1
        if s[i] != seq1[i] :
            j = i+1
            while j<2*n and seq1[j] == s[j] :
                j += 1
            if j < 2*n :
                s[i] , s[j] = seq1[i] , seq1[j]
            	a1 += 1
            else :
            	break
        i  += 1
    print min(a1,a0)