#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
vector<long long>p, q;
int n, d;
bool f(long long x) {
	vector<vector<long long>> dp(d, vector<long long>(n, -LINF));
	rep(i, n) if (-p[i] >= x)dp[0][i] = -p[i] + q[i];
	rep(i, d - 1) {
		vector<long long>maxL(n + 1, -LINF), maxR(n + 1, -LINF);
		rep(j, n)maxL[j + 1] = max(maxL[j], dp[i][j]);
		rep(j, n)maxR[j + 1] = max(maxR[j], dp[i][n - j - 1]);
		rep(j, n) {
			long long mx = max(maxL[j], maxR[n - (j + 1)]);
			mx -= p[j];
			if (mx >= x)dp[i + 1][j] = mx + q[j];
		}
	}
	rep(i, n) if (-LINF != dp[d - 1][i])return true;
	return false;
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin >> n >> d;
	p.resize(n);
	q.resize(n);
	rep(i, n)cin >> p[i] >> q[i];
	long long ok = -LINF - 1;
	long long ng = LINF + 1;
	while (1 < abs(ok - ng)) {
		long long c = (ng + ok) / 2;
		if (f(c)) ok = c;
		else ng = c;
	}
	cout << ok << endl;
	return 0;
}