n,D = map(int,input().split())
PQ = [list(map(int,input().split())) for i in range(n)]
inf = 10**8
def search(x):
    ldp = [0]*(n+1)
    rdp = [0]*(n+1)
    ldp[-1] = rdp[-1] = -inf
    for i in range(D):
        ndp = [-inf]*(n+1)
        for j,(p,q) in enumerate(PQ):
            nex = max(ldp[j-1],rdp[j+1])
            if nex-p >= x:
                ndp[j] = nex-p+q
        for j in range(n):
            ldp[j] = max(ndp[j],ldp[j-1])
            rdp[n-1-j] = max(ndp[n-1-j],rdp[n-j])
    if rdp[0] != -inf:
        return True
    return False



l = -inf
r = 0

while r > l + 1:
    m = (r+l)//2

    if search(m):
        l = m
    else:
        r = m
print(l)