#pragma GCC ta g("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define DEBUG
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    int sz = a.size();
    for(auto itr = a.begin(); itr != a.end(); itr++){
		cout << *itr;
        sz--;
        if(sz) cout << " ";
	}
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){
	cout << a << " " << b << "\n";
}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
void mark() {cout << "#" << "\n";}
ll pcount(ll x) {return __builtin_popcountll(x);}
//#include <atcoder/maxflow>
//using namespace atcoder;
const int inf = (1<<30)-1;
const ll linf = 1LL<<61;
const int MAX = 510000;
int dy[8] = {0,1,0,-1,1,-1,-1,1};
int dx[8] = {-1,0,1,0,1,-1,1,-1};
const double pi = acos(-1);
const double eps = 1e-9;
const int mod = 1e9 + 7;
//const int mod = 998244353;

int main(){
    ll n,d; cin >> n >> d;
    vl p(n),q(n);
    rep(i,n) cin >> p[i] >> q[i];
    ll ok = -1e9, ng = 0;
    vvl dp(2,vl(n,-inf));
    while(ng-ok > 1){
        ll mid = (ok+ng) / 2;
        rep(i,2) rep(j,n) dp[i][j] = -inf;
        rep(i,n){
            if(-p[i] >= mid) dp[0][i] = q[i] - p[i];
        }
        rep(i,d-1){
            rep(j,n) dp[1][j] = -inf;
            int val = *max_element(all(dp[0]));
            int id = max_element(all(dp[0])) - dp[0].begin();
            int val2 = -inf;
            rep(j,n){
                if(j == id) continue;
                chmax(val2,dp[0][j]); 
            }
            rep(j,n){
                if(j == id){
                    if(val2 - p[j] >= mid){
                        chmax(dp[1][j], val2 + q[j] - p[j]);
                    }
                }else{
                    if(val - p[j] >= mid){
                        chmax(dp[1][j], val + q[j] - p[j]);
                    }
                }
            }
            swap(dp[0],dp[1]);
        }
        bool f = false;
        rep(i,n) if(dp[0][i] >= mid) f = true;
        if(f) ok = mid;
        else ng = mid;
    }
    cout << ok << endl;
}