x_a, y_a = map(int, input().split())
x_b, y_b = map(int, input().split())

numerator = x_b * y_a + x_a * y_b
denominator = x_a + x_b
y_p = numerator / denominator

# 处理整数情况下的输出格式，比如第三个样例输出应为514而不是514.0
print(y_p if y_p % 1 != 0 else int(y_p))