from sys import stdin
n, d, *indata = map(int, stdin.read().split())
offset = 0
p = []
q = []
for i in range(n):
    s, t = indata[offset + 2*i],indata[offset + 2*i+1]
    p.append(s)
    q.append(t)

largenum = -10**9
left = -10**8
right = 0
while (right - left) >= 2:
    mid = (right + left) // 2
    dp = [[largenum for i in range(n)] for j in range(d)]
    for i in range(n):
        if -p[i] >= mid:
            dp[0][i] = q[i] - p[i]
    for i in range(1,d):
        ruisekileft = [largenum for i in range(n+1)]
        ruisekiright = [largenum for i in range(n+1)]
        for j in range(n):
            ruisekileft[j+1] = max(ruisekileft[j],dp[i-1][j])
            ruisekiright[j+1] = max(ruisekiright[j],dp[i-1][n-j-1])
        for j in range(n):
            kari = max(ruisekileft[j],ruisekiright[n-j-1])
            if kari - p[j] >= mid:
                dp[i][j] = kari + q[j] - p[j]
    check = False
    for i in range(n):
        if dp[d-1][i] != largenum:
            check = True
            break
    if check:
        left = mid
    else:
        right = mid

print("{}".format(left))