@staticmethod
def d():
    (n, k, *wp) = map(int, sys.stdin.read().split())
    (w, p) = np.array(wp).reshape((- 1), 2).T

    def f(x):
        return np.sort((w * (p - x)))[(- k):].sum()
    print(optimize.bisect(f, 0, 100))
@staticmethod
def d():
    (n, k, *wp) = map(int, sys.stdin.read().split())
    (w, p) = np.array(wp).reshape((- 1), 2).T

    def f(x):
        return np.sort((w * (p - x)))[(- k):].sum()
    print(optimize.bisect(f, 0, 100))