Problem:
Score : 400 points

Problem Statement

We have N points in a two-dimensional plane.

The coordinates of the i-th point (1 \leq i \leq N) are (x_i,y_i).

Let us consider a rectangle whose sides are parallel to the coordinate axes that contains K or more of the N points in its interior.

Here, points on the sides of the rectangle are considered to be in the interior.

Find the minimum possible area of such a rectangle.

Constraints

2 \leq K \leq N \leq 50

-10^9 \leq x_i,y_i \leq 10^9 (1 \leq i \leq N)

x_i≠x_j (1 \leq i<j \leq N)

y_i≠y_j (1 \leq i<j \leq N)

All input values are integers. (Added at 21:50 JST)

Input

Input is given from Standard Input in the following format:

N K
x_1 y_1
:
x_{N} y_{N}

Output

Print the minimum possible area of a rectangle that satisfies the condition.

Sample Input 1

4 4
1 4
3 3
6 2
8 1

Sample Output 1

21

One rectangle that satisfies the condition with the minimum possible area has the following vertices: (1,1), (8,1), (1,4) and (8,4).

Its area is (8-1) × (4-1) = 21.

Sample Input 2

4 2
0 0
1 1
2 2
3 3

Sample Output 2

1

Sample Input 3

4 3
-1000000000 -1000000000
1000000000 1000000000
-999999999 999999999
999999999 -999999999

Sample Output 3

3999999996000000001

Watch out for integer overflows.

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

import sys
import itertools

sr = lambda: sys.stdin.readline().rstrip()
ir = lambda: int(sr())
lr = lambda: list(map(int, sr().split()))

N, K = lr()
XY = [lr() for _ in range(N)]
answer = float('inf')
# 端の4点、まずはx軸の2点を選ぶ
for i, j in itertools.product(list(range(N)), repeat=2):
    xleft = XY[i][0]
    xright = XY[j][0]
    candidate = [(x, y) for x, y in XY if xleft <= x <= xright]
    if len(candidate) < K:
        continue
    candidate.sort(key=lambda z: z[1])
    for s in range(len(candidate) - K + 1):
        yup = candidate[s+K-1][1]
        ylow = candidate[s][1]
    area = (xright - xleft) * (yup - ylow)
    if area < answer:
        answer = area

print(answer)
# 31