import sre_constants
import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (1, 0), (0, -1), (-1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**19
# md = 998244353
md = 10**9+7

def solve(i, j):
    p1, q1 = pq[i]
    p2, q2 = pq[j]
    res = min(-p1+q1-p2, -p1)
    if d & 1:
        a = (-p1+q1-p2+q2)*(d//2)-p1
        res = min(res, a)
        a += p1-q2
        res = min(res, a)
    else:
        a = (-p1+q1-p2+q2)*(d//2)-q2
        res = min(res, a)
        a += p2-q1
        res = min(res, a)
    return res

n, d = LI()
pq = LLI(n)

ans = -inf
for i in range(n):
    for j in range(n):
        if i == j: continue
        ans = max(ans, solve(i, j))

print(ans)