#include <iostream>
#include <algorithm>
using namespace std;

const int inf = 1000000000;
int n, m, p0[1009], p1[1009];

bool ps(int l)
{
	int mx0 = 0, mx1 = -inf, p = 0;
	for (int i = 1; i <= n; i++) {
		int tmx0 = -inf, tmx1 = -inf, tp = 0;
		for (int j = 1; j <= m; j++) {
			int t = mx0;
			if (p == j) t = mx1;
			if (t - p0[j] < l) continue;
			t = t - p0[j] + p1[j];
			if (tmx0 <= t) {
				tmx1 = tmx0;
				tmx0 = t;
				tp = j;
			}
			else if (tmx1 < t)
				tmx1 = t;
		}
		if (!tp) return false;
		mx0 = tmx0; mx1 = tmx1; p = tp;
	}
	return true;
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> m >> n;
	for (int i = 1; i <= m; i++)
		cin >> p0[i] >> p1[i];
	int s = 0, e = inf, md = (s + e) / 2;
	while (s < e) {
		if (ps(-md)) e = md;
		else s = md + 1;
		md = (s + e) / 2;
	}
	cout << -md << '\n';
	return 0;
}