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 i in range(0,t):
    n=int(raw_input());
    str1=raw_input();
    list1=[];
    list2=[];
    list3=[];
    list4=[];
    for j in range(0,(2*n),2):
        if(str1[j]!="B"):
            list1.append(j);
    for k in range(1,(2*n),2):
        if(str1[k]!="G"):
            list2.append(k);
    count1=len(list1);
    for j in range(1,(2*n),2):
        if(str1[j]!="B"):
            list3.append(j);
    for k in range(0,(2*n),2):
        if(str1[k]!="G"):
            list4.append(k);
    count2=len(list3);
    if(count1<count2):
        print(count1);
    else:
        print(count2);