#include<bits/stdc++.h>

#define mem(a,b) memset((a),(b),sizeof(a))
#define m0(a) memset((a),0,sizeof(a))
#define lb(x) ((x)&-(x))
#define lc(x) ((x)<<1)
#define rc(x) (((x)<<1)|1)
#define pb(G,x) (G).push_back((x))
#define For(a,b,c) for(int a=(b);a<=(c);a++)
#define Rep(a,b,c) for(int a=(b);a>=(c);a--)
#define in1(a) a=read()
#define in2(a,b) a=read(), b=read()
#define in3(a,b,c) a=read(), b=read(), c=read()
#define inn(i,n,a) For(i,1,n) a[i]=read();

#define ll long long
#define i128 __int128

using namespace std;
inline int read() {
	int xx= 0;int f= 1;
	char c = getchar();
	while(c<'0'||c>'9') { 
		if(c=='-') f= -1;
		c= getchar();
	}
	while(c>='0'&&c<='9') {
		xx= (xx<<1)+(xx<<3)+(c^48);
		c= getchar();
	}
	return xx*f;
}
#define maxn 1000050
int n;
long double f;
string s;
pair<long double,int> pre[maxn];
void work() {
	cin>>n>>f>>s; 
	s=' '+s;
	For(i,1,n) {
		pre[i].first=pre[i-1].first+(s[i]-'0')-f;
		pre[i].second=i;
	}
	pre[n+1]={0,0};
	sort(pre+1,pre+n+2);
	long double ans=1e188;
	For(i,1,n) {
		long double x=fabsl((pre[i].first-pre[i+1].first)/(pre[i].second-pre[i+1].second));
		ans=min(ans,x);
	}
	int idx=1e9;
	For(i,1,n) {
		long double x=fabsl((pre[i].first-pre[i+1].first)/(pre[i].second-pre[i+1].second));
		if(fabsl(ans-x)<1e-12) idx=min(idx,min(pre[i].second,pre[i+1].second));
	}
	cout<<idx<<'\n';
	For(i,0,n+1) pre[i].first=pre[i].second=0;
}
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	int _;
	cin>>_;
	For(i,1,_) {
		cout<<"Case #"<<i<<": ";
		work();
	}
}