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//seg tree without lazy propagation 

#include<bits/stdc++.h>
using namespace std;

#define FOR(i, x, y) for (int i = (x); i <= (y); i++)
#define forr(i, x, y) for (int i = (x); i < (y); i++)
#define forrl(i, x, y) for (ll i = (x); i < (y); i++)
#define dow(i, x, y) for (int i = (x); i >= (y); i--)

#define mp make_pair
#define F first
#define S second
#define pb push_back
#define siz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define fil(a, b) memset((a), (b), sizeof(a))

typedef long long ll;
typedef unsigned long long ull;

const int MOD=1e9+7;
const double pi=acos(-1);
const int MAX=2*1e5+5;
const int N=1e6+5;
struct ff{
	int a;
	int b;
	int c;
	int least_b;
	int least_c;
};
string s;
ll ans;
ff seg_Tree[4*N];
ll n,x,y; 
bool found;
ff merg(ff l,ff r){
    return {l.a+r.a,l.b+r.b,l.c+r.c,};
}
void build(int id=0,int ns=0,int ne=n-1){   
	if(found ){
		return;
	}
    if(ns==ne){
        seg_Tree[id]={s[ns]=='a',s[ns]=='b',s[ns]=='c'};
        return;
    }
    int left=2*id+1;//left id of seg tree
    int right=left+1;//right id
    int mid= (ns+ne)/2;//mid range
    build(left,ns,mid);
    build(right,mid+1,ne);
    seg_Tree[id]=merg(seg_Tree[left],seg_Tree[right]);
	if(!found&&ne-ns+1>=2&&
	seg_Tree[id].a>seg_Tree[id].b&&
	seg_Tree[id].a>seg_Tree[id].c){
		found=true;
		ans=ne-ns+1;
	}
}
void solve(){
    cin>>n>>s;
    
	found =false;
	build();
	if(found){
		cout<<ans<<endl;
	}else{
		cout<<-1<<endl;
	}
    

}
int main(){
	// #ifndef ONLINE_JUDGE
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
	// #endif
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
	ll t=1;
    //init();
	 cin>>t;
	for (ll i = 1; i <= t; i++)
	{
		// cout<<"Case "<<i<<": ";
		solve();
	}

	return 0;
}