n, d = map(int, raw_input().split())

tsts = []
for i in xrange(n):
    money, friendship = map(int, raw_input().split())
    for i in xrange(len(tsts)):
        t = tsts[i]
        maxi = t['mmax']
        mini = t['mmin']
        if(money < maxi) and (money > mini):
            n = {'mmax' : money + d  if (money + d) < maxi else maxi, 'mmin': money - d if (money - d) > mini else mini, 'f': t['f'] + friendship}
            tsts.append(n)
    tsts.append({'mmax':money + d, 'mmin': money - d, 'f': friendship})

print(max(tsts, key=lambda t: t['f'])['f'])