#include <stdio.h>
#include <math.h>

int m[20];
double val[20];
int N;
int M;
double V;

void Solve(int T)
{
	int i;
	double min, max, mid, ans;
	for (i = 0; i < N; i++)
	{
		scanf("%d %lf", &m[i], &val[i]);
	}
	scanf("%d %lf", &M, &V);
	min = 0;
	max = 1.0;
	M++;
	while (max - min > 1e-8)
	{
		mid = (max + min) / 2;
		for (i = 0, ans = 0; i < N; i++)
		{
			ans += val[i] * pow(1 + mid, M - m[i]);
		}
//		printf("V = .5lf ans = %.5lf\n", V, ans);
		if (ans > V)
		{
			max = mid;
		}
		else
		{
			min = mid;
		}
	}
	printf("Case %d: %.5lf\n\n", T, mid);
}

int main()
{
	int T = 0;
	while (scanf("%d", &N) != -1 && N > 0)
	{
		Solve(++T);
	}
	return 0;
}