// yukicoder: No.236 鴛鴦茶
// 2019.4.14 bal4u

#include <stdio.h>
#include <string.h>

int main()
{
	int A, B, X, Y;
	double x, y;

	scanf("%d%d%d%d", &A, &B, &X, &Y);
	if ((x = Y * (double)A / B) >= X) {
		x = X; y = X * (double)B / A;
	}
	else y = Y;
	printf("%.10lf\n", x + y);
	return 0;
}