#include<bits/stdc++.h>
#define double long double
using namespace std;
typedef pair <double,int> pii;
const double eps=1e-12;
const int N=5e5+10;
pii a[N];
double p,c;
string x;
int t,n,ans;
int main()
{
//	freopen("tii.in","r",stdin);
//	freopen("tii.out","w",stdout);
	cin>>t;
	for(int tt=1;tt<=t;++tt)
	{
		c=2;
		scanf("%d %Lf",&n,&p);
		cin>>x;
		x=" "+x;
		ans=n-1;
		a[0]={};
		for(int i=1;i<=n;++i)
		{
			a[i]={a[i-1].first+x[i]-'0'-p,i};
		}
		sort(a,a+n+1);
		for(int i=1;i<=n;++i)
		{
			c=min(c,fabsl((a[i].first-a[i-1].first)/(a[i].second-a[i-1].second)));
		}
		for(int i=1;i<=n;++i)
		{
			if(fabsl(fabsl((a[i].first-a[i-1].first)/(a[i].second-a[i-1].second))-c)<eps)
			{
				ans=min(ans,min(a[i].second,a[i-1].second));
			}
		}
		printf("Case #%d: %d\n",tt,ans);
	}
}