"""

同じ2種類のみを繰り返すのが最適？


"""

import sys
from sys import stdin
import math

N,D = map(int,stdin.readline().split())

PQ = []

for i in range(N):
    P,Q = map(int,stdin.readline().split())
    PQ.append((P,Q))

ans = float("-inf")

for i in range(N):
    for j in range(N):

        pi,qi = PQ[i]
        pj,qj = PQ[j]

        if i == j:
            continue

        nans = min(-1 * pi , -1*pi + qi - pj)

        last = (-pi+qi-pj+qj) * (D//2) + (-pi+qi) * (D % 2)

        if D % 2 == 0:
            nans = min(nans , last-qj , last-qj+pj-qi)
        else:
            nans = min(nans , last-qi , last-qi+pi-qj)

        ans = max(ans , nans)

print (ans)