#include <bits/stdc++.h>
using namespace std;
int main() {
int y;cin>>y;while(y--){
int x,n=0;
string l,a,b,f;cin>>x;cin>>l;f==l;
reverse(f.begin(),f.end());if(l==f) cout<<0<<"\n";else{
if(x%2!=0){
x=x/2;a=l.substr(0,x);b=l.substr(x+1,x);}
else{
x=x/2;a=l.substr(0,x);b=l.substr(x,x);
}
reverse(b.begin(),b.end());
for(int i=0;i<x;i++){
if(a[i]!=b[i]) n++;
}
n=(n+1)/2;
cout<<n<<"\n";}
}
return 0;
}
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