#include <stdio.h>

typedef struct {
	int key, id;
} data;

void merge_sort(int n, data x[])
{
	static data y[1001] = {};
	if (n <= 1) return;
	merge_sort(n / 2, &(x[0]));
	merge_sort((n + 1) / 2, &(x[n/2]));
	
	int i, p, q;
	for (i = 0, p = 0, q = n / 2; i < n; i++) {
		if (p >= n / 2) y[i] = x[q++];
		else if (q >= n) y[i] = x[p++];
		else y[i] = (x[p].key < x[q].key)? x[p++]: x[q++];
	}
	for (i = 0; i < n; i++) x[i] = y[i];
}

int main()
{
	int i, N, D, P[1001], Q[1001];
	data d[1001];
	scanf("%d %d", &N, &D);
	for (i = 1; i <= N; i++) {
		scanf("%d %d", &(P[i]), &(Q[i]));
		d[i-1].key = Q[i] - P[i];
		d[i-1].id = i;
	}
	merge_sort(N, d);

	int j, k, l = 1, r = 1 << 27, m, last;
	while (l < r) {
		m = (l + r) / 2;
		for (i = 1, k = 0, last = N; i <= D; i++) {
			for (j = N - 1; j >= 0; j--) {
				if (j == last) continue;
				if (k - P[d[j].id] >= -m) break;
			}
			if (j < 0) break;
			last = j;
			j = d[j].id;
			k += Q[j] - P[j];
		}
		if (i > D) r = m;
		else l = m + 1;
	}
	printf("%d\n", -l);
	fflush(stdout);
	return 0;
}