#include<bits/stdc++.h>
#define MAXN (500005)
#define ll long long
#define db double
#define pi pair<int,int>
#define fi first
#define se second
using namespace std;
const int lim=500000;
const db eps=1e-8;
template<typename type>
void read(type &x)
{
    bool f=0;char ch=0;x=0;
    while(ch<'0'||ch>'9'){f|=!(ch^'-');ch=getchar();}
    while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+(ch^48);ch=getchar();}
    x=f?-x:x;
}
template<typename type,typename... Args>
void read(type &x,Args &... args)
{
    read(x);
    read(args...);
}
char str[MAXN];
int test,n,l,r,now,cas;
int s[MAXN];
db p;
struct node{
	db a;int b;
	inline bool operator<(const node &rsh)const{return a<rsh.a;}
};
set<node> st;
inline void upd_ans(int nl,int nr)
{
    if(l==-1) l=nl,r=nr;
    else if(fabs((s[r]-s[l-1])*1.0/(r-l+1)-p)>fabs((s[nr]-s[nl-1])*1.0/(nr-nl+1)-p)||(fabs(fabs((s[r]-s[l-1])*1.0/(r-l+1)-p)-fabs((s[nr]-s[nl-1])*1.0/(nr-nl+1)-p))<eps&&nl<l)) l=nl,r=nr;
}
void solve()
{
    read(n);scanf("%lf",&p);
    scanf("%s",str+1);
    for(int i=1;i<=n;i++) s[i]=s[i-1]+(str[i]=='1');
    st.clear();l=-1,now=0;
    for(int i=1;i<=n;i++)
    {
        st.insert({now+p*(1-i),i});
        if(str[i]=='1') ++now;
        auto it=st.lower_bound({now-p*i,0});
        if(it!=st.end()) upd_ans((*it).b,i);
        if(it!=st.begin()) --it,upd_ans((*it).b,i);
    }
    printf("Case #%d: %d\n",++cas,l-1);
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen(".in","r",stdin);
    freopen(".out","w",stdout);
#endif
    read(test);
    for(int i=1;i<=test;i++) solve();
}