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:
def main():
    n = int(raw_input())
    s = []
    Str = []
    for i in range(0, n):
        s.append(int(raw_input())*2)
        Str.append(raw_input())
    for i in range(0, n):
        count = 0
        for j in range(0,s[i]):
            if(Str[i][j] == 'B' and j%2==0):
                count+=1
            if(Str[i][j] == 'G' and j%2!=0):
                count+=1
        if count < (s[i]-count):
            print(int(count/2))
        else:
            print(int((s[i]-count)/2))
            
            
    
    
    
if __name__ == '__main__': main()