/*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]<<" ";
    }
    // cout<<endl;
    a[0]=mk(0.0,0);
    sort(a+1,a+n+1);
    for(int i=1;i<=n;i++){
        int x=a[i].se,y=a[i-1].se;
        if(x>y)swap(x,y);
        if(fabsl(1.0*(sum[y]-sum[x])/(y-x))<minn)minn=fabsl(1.0*(sum[y]-sum[x])/(y-x)),ans=x+1;
        else if(fabsl(fabsl(1.0*(sum[y]-sum[x])/(y-x))-minn)<eps)ans=min(ans,x+1);
    }
		cout<<"Case #"<<m<<": ";
		cout<<ans-1<<endl;
	}
    I_love_Furina forever;
}