#include <bits/stdc++.h>
/*
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using bint = mp::cpp_int;
*/
#include <atcoder/all>
#include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <random>
#include <bitset>
#define rep(i,n) for (int i = 0; i < int(n); ++i)
#define repp(i,n,m) for (int i = m; i < int(n); ++i)
#define repb(i,n) for (int i = int(n)-1; i >= 0; --i)
#define fi first
#define se second
#define endl "\n"
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using P = pair<int, int>;
using PL = pair<long long, long long>;
using Pxy = pair<long double, long double>;
using pil = pair<int,ll>;
using pli = pair<ll,int>;
const int INF = 1001001007;
const long long mod1 = 1000000007LL;
const long long mod2 = 998244353LL;
const ll inf = 2e18;
const ld pi = 3.14159265358979323;
const ld eps = 1e-7;
template<class T>istream &operator>>(istream &is,vector<T> &v){for(auto &e:v)is>>e;return is;}
template<class T>ostream &operator<<(ostream &os,const vector<T> &v){if(v.size()==0){os<<endl;}else{rep(i,v.size())os<<v[i]<<(i+1==v.size()?"\n":" ");}return os;}
template<class T>istream &operator>>(istream &is,vector<vector<T>> &v){for(auto &e:v)is>>e;return is;}
template<class T>ostream &operator<<(ostream &os,const vector<vector<T>> &v){if(v.size()==0){os<<endl;}else{for(auto &e:v)os<<e;}return os;}
template<typename T>bool range(T a,T b,T x){return (a<=x&&x<b);}
template<typename T>bool rrange(T a,T b,T c,T d,T x,T y){return (range(a,c,x)&&range(b,d,y));}
template<typename T>void rev(vector<T> &v){reverse(v.begin(),v.end());}
template<typename T>void sor(vector<T> &v, int f=0){sort(v.begin(),v.end());if(f!=0) rev(v);}
template<typename T>bool chmin(T &a,const T &b){if(a>b){a=b;return true;}return false;}
template<typename T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<typename T>void eru(vector<T> &v){sor(v);v.erase(unique(v.begin(),v.end()),v.end());}
template<typename T>T cel(T a,T b){if(a%b==0)return a/b;return a/b +1;}
template<typename T,typename U>void out2(T a,U b){cout<<a<<" "<<b<<endl;}
template<typename T>void mout(T a){cout<<a.val()<<endl;}
void yes(){cout << "Yes" << endl;}
void no (){cout << "No" << endl;}
void yn (bool t){if(t)yes();else no();}
void dame(bool t){if(t){cout << -1 << endl;exit(0);}}
void dout(ld h=-1.23456789){cout<<setprecision(20);if(abs(h+1.23456789)>eps)cout<<h<<endl;}
void deb(ll h = INF-1) {cout << (h == INF-1 ? "!?" : to_string(h)) << endl;}
void revs(string &s) {reverse(s.begin(),s.end());}
vector<int> dx = {0,1,0,-1};
vector<int> dy = {1,0,-1,0};
const string ALP = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string alp = "abcdefghijklmnopqrstuvwxyz";
const string num = "0123456789";

ll gcds(ll a, ll b){
    a = abs(a); b = abs(b);
    if (b == 0) return a;
    ll c = a % b;
    while (c != 0){
        a = b;
        b = c;
        c = a % b;
    }
    return b;
}

ll tentou(vector<ll> ar){
    int n = ar.size();
    set<ll> st;
    rep(i,n) st.insert(ar[i]);
    map<ll,int> mp;
    int ind = 0;
    for (ll x : st){
        mp[x] = ind;
        ind++;
    }
    fenwick_tree<ll> fw(ind);
    ll ans = 0;
    rep(i,n){
        int a = mp[ar[i]];
        ans += i - fw.sum(0,a+1);
        fw.add(a,1);
    }
    return ans;
}

/*
alias g++='g++ -I/mnt/c/Users/Owner/Desktop/ac-library'
*/

struct vs{
    vector<int> to;
};

int main(){
    ll n, d; cin >> n >> d;
    vector<PL> ar(n);
    rep(i,n) cin >> ar[i].first >> ar[i].second;
    ll ans = -inf;
    rep(i,n) rep(j,n){
        if (i == j) continue;
        ll mi = 0;
        ll ima = 0;
        ima -=  ar[i].first; chmin(mi,ima);
        ima += ar[i].second; chmin(mi,ima);
        ima -=  ar[j].first; chmin(mi,ima);
        ima += ar[j].second; chmin(mi,ima);
        if (d == 1) chmax(ans,-ar[i].first);
        else if (ima >= 0) chmax(ans,mi);
        else {
            ll ti = (d - 2) / 2;
            ima *= ti;
            rep(k,d-ti*2){
                if (k % 2 == 0){
                    ima -=  ar[i].first; chmin(mi,ima);
                    ima += ar[i].second; chmin(mi,ima);
                }
                else {
                    ima -=  ar[j].first; chmin(mi,ima);
                    ima += ar[j].second; chmin(mi,ima);
                }
            }
            chmax(ans,mi);
        }
    }
    cout << ans << endl;
}