#####segfunc#####
def segfunc(x, y):
    return max(x,y)
#################

#####ide_ele#####
ide_ele = -float('inf')
#################

class SegTree:
    """
    init(init_val, ide_ele): 配列init_valで初期化 O(N)
    update(k, x): k番目の値をxに更新 O(logN)
    query(l, r): 区間[l, r)をsegfuncしたものを返す O(logN)
    """
    def __init__(self, init_val, segfunc, ide_ele):
        """
        init_val: 配列の初期値
        segfunc: 区間にしたい操作
        ide_ele: 単位元
        n: 要素数
        num: n以上の最小の2のべき乗
        tree: セグメント木(1-index)
        """
        n = len(init_val)
        self.segfunc = segfunc
        self.ide_ele = ide_ele
        self.num = 1 << (n - 1).bit_length()
        self.tree = [ide_ele] * 2 * self.num
        # 配列の値を葉にセット
        for i in range(n):
            self.tree[self.num + i] = init_val[i]
        # 構築していく
        for i in range(self.num - 1, 0, -1):
            self.tree[i] = self.segfunc(self.tree[2 * i], self.tree[2 * i + 1])

    def update(self, k, x):
        """
        k番目の値をxに更新
        k: index(0-index)
        x: update value
        """
        k += self.num
        self.tree[k] = x
        while k > 1:
            self.tree[k >> 1] = self.segfunc(self.tree[k], self.tree[k ^ 1])
            k >>= 1

    def query(self, l, r):
        """
        [l, r)のsegfuncしたものを得る
        l: index(0-index)
        r: index(0-index)
        """
        res = self.ide_ele

        l += self.num
        r += self.num
        while l < r:
            if l & 1:
                res = self.segfunc(res, self.tree[l])
                l += 1
            if r & 1:
                res = self.segfunc(res, self.tree[r - 1])
            l >>= 1
            r >>= 1
        return res
    def value(self,index):
        return self.query(index,index+1)
N,D = map(int,input().split())
P = []
Q = []
for _ in range(N):
    p,q = map(int,input().split())
    P.append(p)
    Q.append(q)

def is_ok(x):
    INF = float('inf')
    tmp = [0 for _ in range(N)]
    for i in range(1,D+1):
        new = [-INF for _ in range(N)]
        if i == 1:
            for k in range(N):
                if -P[k] < x:
                    new[k] = -INF
                else:
                    new[k] = Q[k] - P[k]
            seg = SegTree(new,segfunc,ide_ele)
        else:
            for k in range(N):
                if -P[k] + max(seg.query(0,k),seg.query(k+1,N)) < x:
                    new[k] = -INF
                else:
                    new[k] = max(seg.query(0,k),seg.query(k+1,N)) + Q[k] - P[k]
            seg = SegTree(new,segfunc,ide_ele)
    return seg.query(0,N) > -INF
ng = 0
ok = -10 ** 8
while ng - ok > 1:
    x = (ng+ok) //2
    if is_ok(x):
        ok = x
    else:
        ng = x
print(ok)