#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000000000


int main(){
	
	int N,D;
	cin>>N>>D;
	
	vector<int> p(N),q(N);
	rep(i,N)cin>>p[i]>>q[i];
	long long ans = -Inf;
	rep(i,N){
		rep(j,N){
			if(i==j)continue;
			
			long long cur = 0LL,mini = 0LL;
			cur -= p[i];
			mini = min(mini,cur);
			cur += q[i];
			cur -= p[j];
			mini = min(mini,cur);
			cur += q[j];
			long long DD = D;
			DD -= 2;
			
			int X = DD / 2;
			X = max(0,X-2);
			DD -= X * 2;
			cur += cur * X;
			rep(k,DD){
				if(k%2==0){
					cur -= p[i];
					mini = min(mini,cur);
					cur += q[i];
				}
				else{
					cur -= p[j];
					mini = min(mini,cur);
					cur += q[j];
				}
			}
			ans = max(ans,mini);
		}
	}
	cout<<ans<<endl;
	
	return 0;
}