from collections import *
from itertools import *
import sys


def debug(*args, end="\n"):
    print(*args, end=end, file=sys.stderr)


sys.setrecursionlimit(10 ** 6)
MOD = 998244353

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

menus = sorted(menus, key=lambda x: (x[0], -x[1]))
ans = 0
cur = 0
for p, q in menus[:D]:
    cur -= p
    ans = min(ans, cur)
    cur += q
print(ans)
debug("ans")