#include<bits/stdc++.h>
using namespace std;
const int N=5e5+5;
int n;
int a[N],sx[N],sy[N];
double f[N],p;
set<pair<double,int> >S;
int main(){
//	freopen("tii.in","r",stdin);
//	freopen("tii.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	int _;
	cin>>_;
	for(int t=1;t<=_;t++){
		cin>>n>>p;
		for(int i=1;i<=n;i++){
			char x;
			cin>>x;
			a[i]=x-'0';
			sx[i]=sx[i-1]+a[i];
			sy[i]=sy[i-1]+1;
		}
		for(int i=0;i<=n;i++)
			f[i]=sx[i]-p*sy[i]; 
		S.clear();
		double ans=1e9;
		int al=n;
		for(int i=n;i;i--){
			S.insert(make_pair(f[i],i));
			auto R=S.upper_bound(make_pair(f[i-1],114514)),L=R;
			if(R!=S.end()){
				int l=i,r=(*R).second;
				double ret=(sx[r]-sx[l-1])/1.0/(sy[r]-sy[l-1]);
				if(fabs(ret-p)<=fabs(ans-p)){
					ans=ret;
					al=l;
				}
			}
			if(R!=S.begin()){
				L--;
				int l=i,r=(*L).second;
				double ret=(sx[r]-sx[l-1])/1.0/(sy[r]-sy[l-1]);
				if(fabs(ret-p)<=fabs(ans-p)){
					ans=ret;
					al=l;
				}
			}
		}
		cout<<"Case #"<<t<<": "<<al-1<<'\n';
	}
	return 0;
}
/*
1
10 0.827672
0010101011
*/