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:
for _ in range(input()):
        n=input()
        b=raw_input()
        s1=['G']*(2*n)
        s2=['G']*(2*n)
        j=count1=count2=0
        for i in xrange(1,2*n,2):
                s1[i]='B'
                s2[j]='B'
                j=j+2
        for i in xrange(2*n):
                if b[i]!=s1[i]:
                        count1+=1
                if b[i]!=s2[i]:
                        count2+=1
        print min(count1/2,count2/2)