## https://yukicoder.me/problems/no/1715

from collections import deque

def check(N, D, pq, border):
    # 料理に対するborderを求める
    borders = []
    for i, (p, q) in enumerate(pq):
        borders.append((border + p, i))
    borders.sort(reverse=True, key=lambda x: x[0])

    dp = [[-float("inf")] * (N + 1) for _ in range(D + 1)]
    dp[0][0] = 0
    for d in range(1, D + 1):
        array = [(i, dp[d - 1][i]) for i in range(N + 1)]
        array.sort(reverse=True, key=lambda x: x[1])

        ind = 0
        queue = deque()
        for b, i in borders:
            while ind < N + 1 and array[ind][1] >= b:
                if len(queue) == 0 or array[ind][1] > queue[0][1]:
                    queue.appendleft(array[ind])
                else:
                    while len(queue) > 1 and queue[-1][1] < array[ind][1]:
                        queue.pop()
                    queue.append(array[ind])
                ind += 1                    

            if len(queue) == 0:
                continue
            elif len(queue) == 1:
                if queue[0][0] != i + 1:
                    dp[d][i + 1] = queue[0][1] + pq[i][1] - pq[i][0]
            else:
                if queue[0][0] != i + 1:
                    dp[d][i + 1] = queue[0][1] + pq[i][1] - pq[i][0]
                else:
                    dp[d][i + 1] = queue[1][1] + pq[i][1] - pq[i][0]

    ans = -float("inf")
    for i in range(N + 1):
        ans = max(dp[D][i], ans)
    return ans != - float("inf")


def main():
    N, D = map(int, input().split())
    pq = []
    for _ in range(N):
        p, q = map(int, input().split())
        pq.append((p, q))
    
    low = -10 ** 9
    high = 10 ** 9
    while high - low > 1:
        mid = (low + high) // 2
        if check(N, D, pq, mid):
            low = mid
        else:
            high = mid

    if check(N, D, pq, high):
        print(high)
    else:
        print(low)




if __name__ == "__main__":
    main()