#include <bits/stdc++.h>
using namespace std;

#define rep(i, x) for(int i = 0; i < (x); i++)

const int inf = 1 << 29;

int main() {
	int n, d;
	cin >> n >> d;
	vector<int> p(n), q(n);
	rep(i, n) { cin >> p[i] >> q[i]; }

	auto f = [&](int x) {
		vector dp(d + 1, vector(n, -inf));
		rep(i, n) {
			if(-p[i] < x) continue;
			dp[1][i] = q[i] - p[i];
		}
		for(int i = 1; i < d; i++) {
			auto vec = dp[i];
			auto mx = -inf, mx2 = -inf;
			rep(j, n) {
				if(mx < dp[i][j]) {
					mx2 = mx, mx = dp[i][j];
				} else if(mx2 < dp[i][j]) {
					mx2 = dp[i][j];
				}
			}
			rep(j, n) {
				if(dp[i][j] != mx) {
					if(mx - p[j] < x) continue;
					dp[i + 1][j] = mx - p[j] + q[j];
				} else {
					if(mx2 - p[j] < x) continue;
					dp[i + 1][j] = mx2 - p[j] + q[j];
				}
			}
		}
		return *max_element(dp.back().begin(), dp.back().end()) > -inf;
	};

	int ok = -inf, ng = inf;
	while(abs(ok - ng) > 1) {
		int mid = (ok + ng) / 2;
		(f(mid) ? ok : ng) = mid;
	}
	cout << ok << endl;
	
	return 0;
}