#include<bits/stdc++.h>
#define rep(i,a,n) for(int i=(a);i<=(n);++i)
#define per(i,a,n) for(int i=(n);i>=(a);--i)
#define SZ(x) ((int)(x).size())
#define eps 1e-12

using namespace std;
typedef long double db;
typedef long long ll;
typedef pair<int,int> pii;

const int maxn=5e5+10;

int n,id[maxn];
db p,a[maxn];
char s[maxn];

inline void solve(){
	scanf("%d%Lf%s",&n,&p,s+1);	
	rep(i,1,n){
		id[i]=i;
		a[i]=a[i-1]+(s[i]=='1')-p;
	}
	id[0]=a[0]=0;
	sort(id,id+1+n,[&](const int &x,const int &y){
		return a[x]<a[y];
	});
	db res=10000000000000000;
	rep(i,1,n){
		res=min(res,fabsl((a[id[i]]-a[id[i-1]])/(id[i]-id[i-1])));
	}
	int lef=n+1;
	rep(i,1,n){
		if(fabsl((a[id[i]]-a[id[i-1]])/(id[i]-id[i-1]))-res<eps){
			lef=min(lef,min(id[i],id[i-1]));
		}
	}
	printf("%d\n",lef);
}

signed main(){
    int _=1;
    scanf("%d",&_); 
   	rep(t,1,_){
   		printf("Case #%d: ",t);
   		solve();
	}
}