def solve():
    n=int(input())
    s=input()
    one=0
    zero=0
    for x in s:
        one+=(x=='1')
        zero+=(x=='0')
    ans1=0
    ans2=0
    for i in range(one):
        if(s[i]=='0'):
            ans1+=1
    for i in range(zero):
        if(s[i]=='1'):
            ans2+=1
    print(min(ans1,ans2))

t = int(input())
for _ in range(t):
    solve()