#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx,popcnt,sse4,abm")
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define X first
#define Y second
int n;int m;
int ans;
pair<int,int>ar[500005];
void solve(int st){
multiset<int>mst;
int sum=0;
for(int i=st-1;i>=st-m+2;i--){
mst.insert(ar[i].second);
sum+=ar[i].second;
}
for(int i=st-m+1;i>=1;i--){
int cal=sum+ar[st].second-ar[st].first*2;
cal+=ar[i].first*2+ar[i].second;
ans=max(ans,cal);
mst.insert(ar[i].second);
sum+=ar[i].second;
sum-=*(mst.begin());
mst.erase(mst.begin());
}
}
signed main(){
cin>>n>>m;
for(int i=1;i<=n;i++){
cin>>ar[i].second>>ar[i].first;
}
sort(ar+1,ar+n+1);
ans=-1e12;
for(int i=m;i<=n;i++){
solve(i);
}
cout<<ans<<endl;
}
