View Code of Problem 1091

/*110ms,192KB*/

#include <cstdio>
#include <cmath>

int main(void)
{
	double ka, acid;
	int m, n;
	while (scanf("%lf%lf%d%d", &ka, &acid, &m, &n), m)
		printf("%.3f\n", -log10((-ka + sqrt(ka * ka + (m << 2) * n * acid * ka)) / (n << 1)));
	return 0;
}