n, d = map(int, input().split())
pq = []
ans = -10 ** 18
pq = list(tuple(map(int, input().split())) for _ in range(n))

l = -10 ** 9
r = 0
while r - l > 1:
    c = (l + r) // 2
    dp = [0] * n
    for _ in range(d):
        ndp = [-10 ** 9] * n
        mx = -10 ** 9
        imx = -1
        for i in range(n):
            if dp[i] > mx:
                mx = dp[i]
                imx = i
        for i, (p, q) in enumerate(pq):
            if i != imx and mx - p >= c:
                ndp[i] = mx - p + q
        p, q = pq[imx]
        for i in range(n):
            if i != imx and dp[i] - p >= c:
                ndp[i] = max(ndp[i], dp[i] - p + q)
        dp = ndp
    if max(dp) == -10 ** 9:
        r = c
    else:
        l = c
print(l)