#include<bits/stdc++.h>
using namespace std;
void solve()
{
    int n; cin>>n;
    string s; cin>>s;
    int one=0,zero=0;
    for(auto x:s) one+=(x=='1'), zero+=(x=='0');
    int ans1=0,ans2=0;
    for(int i=0;i<one;i++)
    {
        if(s[i]=='0') ans1++;
    }
    for(int i=0;i<zero;i++)
    {
        if(s[i]=='1') ans2++;
    }
    cout<<min(ans1,ans2)<<endl;
}

int main(){int t; cin>>t; while(t--) solve();}