/*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 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=1e9;
		for(int i=1;i<=n;i++){
			if(s[i-1]=='1')sum[i]=sum[i-1]+1.0;
			else sum[i]=sum[i-1];
			a[i].fi=sum[i]-i*f;
			a[i].se=i;
		}
		sort(a+1,a+n+1);
		for(int i=1;i<n;i++){
			for(int j=i+1;j<=min(i+100,n);j++){
				int x=a[i].se,y=a[j].se;
				if(x>y)swap(x,y);
				if(fabs(1.0*(sum[y]-sum[x-1])/(y-x+1)-f)<minn)minn=fabs(1.0*(sum[y]-sum[x-1])/(y-x+1)-f),ans=x;
				else if(fabs(fabs(1.0*(sum[y]-sum[x-1])/(y-x+1)-f)-minn)<eps)ans=min(ans,x);
			}
		}
		cout<<"Case #"<<m<<": ";
		cout<<ans-1<<endl;
	}
    I_love_Furina forever;
}