#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define sz(a) (int)(a.size())
#define all(a) a.begin(),a.end()
#define lb lower_bound
#define ub upper_bound
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
#define MOD (ll)(998244353)
#define INF (ll)(5e18)
#define debug(...) fprintf(stderr, __VA_ARGS__),fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false);\
debug("%s time : %.4fs\n", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
typedef long long int ll;
typedef long double ld;
typedef pair<ll,ll> PII;
typedef pair<int,int> pii;
typedef vector<vector<int>> vii;
typedef vector<vector<ll>> VII;
int main(){
int n,m;
cin>>n>>m;
vector<PII>v(n);
for(int i=0;i<n;i++)cin>>v[i].se>>v[i].fi;
sort(all(v));
ll ans = -1e18;
for(int i=m-1;i<n;i++){
ll sum = v[i].se - 2*v[i].fi; //right endpoint
priority_queue<ll,vector<ll>,greater<ll>>pq; //pq stores middle m-2 elememts
for(int j=i-1;j>=i-m+2;j--){
sum+=v[j].se;
pq.push(v[j].se);
}
for(int j=i-m+1;j>=0;j--){
ans = max(ans,sum+v[j].se + 2*v[j].fi); //leftendpoint
if(v[j].se > pq.top()){
sum+=v[j].se;
sum-=pq.top();
pq.pop();
pq.push(v[j].se);
}
}
}
cout<<ans;
}
