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
    for i in 1..D:
        for j in 1..N:
            dp[i][j] = q
        for j in 1..N:
            for k in 1..N:
                if j == k: continue
                if dp[i-1][k] - P[j] >= t:
                    dp[i][j] = max(dp[i][j], dp[i-1][k] - P[j] + Q[j])
    var f = false
    for i in 1..N:
        if dp[D][i] > q:
            f = true
    if f:
        l = t
    else:
        r = t
echo l