import sequtils,strutils
var
    N,D: int
    P, Q: array[1010, int]
    dp : array[1010, array[1010, int]]
var input = stdin.readLine.split.map(parseInt)
(N, D) = (input[0], input[1])

for n in 1..N:
    input = stdin.readLine.split.map(parseInt)
    (P[n], Q[n]) = (input[0], input[1])
var
    r = 0
    l = -100000001
    q = -100000000001
while r - l > 1:
    var t = (r + l) div 2
    var f = false
    for i in 1..D:
        f = false
        for j in 1..N:
            dp[i][j] = q
        var k, mk : int
        mk = q
        for j in 1..N:
            if dp[i-1][j] > mk:
                k = j
                mk = dp[i-1][j]
        f = false
        for j in 1..N:
            if j == k: continue
            if mk - P[j] >= t:
                dp[i][j] = mk - P[j] + Q[j]
                f = true
            if dp[i - 1][j] - P[k] >= t:
                dp[i][k] = max(dp[i - 1][j] - P[k] + Q[k], dp[i][k])
                f = true
        if f == false:
            break
    if f:
        l = t
    else:
        r = t
echo l