#include<stdio.h>
#include<math.h>
int main()
{
    int i,j,n,k,a[13],tm,t=0;
    double b[13],ts,r,p,sum1,sum2;
    while(scanf("%d",&n),n!=-1)
    {
        if(t)printf("\n");
        for(i=1;i<=n;i++)scanf("%d %lf",&a[i],&b[i]);
        scanf("%d %lf",&tm,&ts);
        r=0;sum1=0;
        for(k=1;k<=n;k++)if(a[k]<=tm)sum1+=b[k]*pow(2,tm-a[k]+1); 
        if(fabs(ts-sum1)<1e-8)r=1;
        else
        for(i=1;i<15;i++)
        {
            p=pow(0.1,i);sum1=sum2=0;
            for(k=1;k<=n;k++)if(a[k]<=tm)sum1+=b[k]*pow(1+r,tm-a[k]+1);       
              for(j=1;j<=10;j++)
              {
                sum2=0;  
                for(k=1;k<=n;k++)if(a[k]<=tm)sum2+=b[k]*pow(1+r+p*j,tm-a[k]+1);
                if(sum1-ts<0&&sum2-ts>0){r+=p*(j-1);break;}
                sum1=sum2;
              }    
        }
        t++;    
        printf("Case %d: %0.5lf\n",t,r);
    }    
    return 0;
}