/*Life is too long to end at a grave*/
#include<bits/stdc++.h>
#define N 1000010
#define I_love_Furina return
#define forever 0
#define foreverr 1
#define endl '\n'
#define FIO(s) do{freopen(s".in","r",stdin);freopen(s".out","w",stdout);}while(false)
#define IOS ios::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define db long double
#define ull unsigned long long
#define chc cout<<114514<<endl
#define PDI pair<db,int>
#define fi first
#define se second
#define mk make_pair
#define eps 1e-12
#define int long long
using namespace std;
int n,T,m;
db f,sum[N];
PDI a[N];
string s;
signed main(){
    IOS;//FIO("");
	cin>>T;
	while(T--){
		m++;
		cin>>n>>f>>s;
		int ans=1e12;
		db minn=1e12;
		n=s.length();
		for(int i=1;i<=n;i++){
			sum[i]=sum[i-1]+(s[i-1]-'0')-f;
			a[i].fi=sum[i];
			a[i].se=i;
			// cout<<sum[i]<<" ";
		}
		a[0]=mk(0.0,0);
		// cout<<endl;
		sort(a,a+n+1);
		for(int i=1;i<=n;i++){
			int x=a[i].se,y=a[i-1].se;
			minn=min(minn,fabsl(1.0*(sum[y]-sum[x])/(y-x)));
		}
		for(int i=1;i<=n;i++){
			int x=a[i].se,y=a[i-1].se;
			if(fabsl(fabsl((sum[y]-sum[x])/(y-x))-minn)<eps)ans=min(ans,min(x,y)+1);
		}
		cout<<"Case #"<<m<<": ";
		cout<<ans-1<<endl;
	}
    I_love_Furina forever;
}