from itertools import combinations



N, D = map(int, input().split())
P = []
Q = []
for _ in range(N):
    p, q = map(int, input().split())
    P.append(p)
    Q.append(q)

result = -1001001001001001001

for i, j in combinations(range(N), 2):
    pi, qi = P[i], Q[i]
    pj, qj = P[j], Q[j]
    ans = -1001001001001001001
    if qi+qj-pi-pj >= 0:
        ans = max(min(-pi-pj+qi, -pi), min(-pj-pj+qj, -pj))
    else:
        ii, jj = qi-pi, qj-pj
        if N % 2 == 0:
            now = ii * (N-1) // 2 + jj * (N-1) // 2
            ans = now + max(-pi-pj+qi, -pi-pj+qj)
        else:
            now = ii * N // 2 + jj * N // 2
            ans = now + max(-pi, -pj)
    result = max(result, ans)
print(result)