#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 ok = -1000000000, ng = 0;
	while(ng-ok>1LL){
		long long mid = (ok+ng)/2;
		
		vector<long long> dp(N,0);
		
		rep(i,D){
			vector<long long> ndp(N,-Inf);
			long long cur = -Inf;
			rep(j,N){
				if(cur - p[j] >= mid){
					ndp[j] = max(ndp[j],cur - p[j] + q[j]);
				}
				cur = max(cur,dp[j]);
			}
			cur = -Inf;
			for(int j=N-1;j>=0;j--){
				if(cur - p[j] >= mid){
					ndp[j] = max(ndp[j],cur - p[j] + q[j]);
				}
				cur = max(cur,dp[j]);
			}
			swap(dp,ndp);
		}
		long long M = -Inf;
		rep(i,N)M = max(M,dp[i]);
		if(M!=-Inf)ok = mid;
		else ng = mid;
		
		
	}
	
	cout<<ok<<endl;
	
	return 0;
}