#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define P pair<ll,ll>
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) UB(A,x)-LB(A,x)
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
using mint=modint1000000007;
//using mint=modint998244353;
signed main(){
  ll N,D,ans=-1e18;cin>>N>>D;
  vector<ll>p(N),q(N);REP(i,N)cin>>p[i]>>q[i];
  ll m=1e18;REP(i,N)m=min(m,p[i]);
  REP(i,N)REP(j,N)if(i!=j){
    ll t=q[i]+q[j]-p[i]-p[j],res;
    if(t<0){
      ll k=t*(D/2);
      if(D%2)res=min(k-q[i],k-m);
      else res=min(k-q[j],k-q[i]-q[j]+p[j]);
    }
    else res=min(-p[i],q[i]-p[i]-p[j]);
    ans=max(ans,res);
  }
  cout<<ans<<endl;
  return 0;
}