#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cassert>
#include <map>
using namespace std;
using ll = long long;
#define MIN(a, b) (((a) < (b)) ? (a) : (b))
#define MAX(a, b) (((a) < (b)) ? (b) : (a))
int const nmax = 400000;
ll const inf = 1000000000000000000;
pair<int,int> v[5 + nmax];
map<ll,ll> code, decode;
void normalize(int n){
vector<int> temp;
for(int i = 1;i <= n; i++)
temp.push_back(v[i].second);
sort(temp.begin(), temp.end());
temp.erase(unique(temp.begin(), temp.end()), temp.end());
for(int i = 0; i < temp.size(); i++) {
code[temp[i]] = 1 + i;
decode[i + 1] = temp[i];
}
for(int i = 1;i <= n; i++)
v[i].second = code[v[i].second];
}
class SegmentTree{
private:
vector<pair<int, ll>> aint;
pair<int, ll> _add(pair<int, ll> f1, pair<int,ll> f2){
return {f1.first + f2.first, f1.second + f2.second};
}
public:
SegmentTree(int n){
aint.resize(1 + 4 * n);
}
void computenode(int node, int from, int to){
aint[node] = _add(aint[node * 2], aint[node * 2 + 1]);
}
void update(int node, int from, int to, int x, pair<int, ll> val){
if(from < to){
int mid = (from + to) / 2;
if(x <= mid)
update(node * 2, from, mid, x, val);
else
update(node * 2 + 1, mid + 1, to, x, val);
computenode(node, from, to);
} else
aint[node] = _add(aint[node], val);
}
ll query(int node, int from, int to, int k){
if(aint[node].first < k)
return -inf;
if(from < to){
int mid = (from + to) / 2;
if(k <= aint[node * 2 + 1].first)
return query(node * 2 + 1, mid + 1, to, k);
else
return query(node * 2, from, mid , k - aint[node * 2 + 1].first) + aint[node * 2 + 1].second;
} else
return 1LL * decode[from] * k;
}
int _size(){
return aint[1].first;
}
};
int n, k;
ll result = -inf;
void _insert(SegmentTree &aint, int val){
aint.update(1, 1, n, val, {1, decode[val]});
}
void _erase(SegmentTree &aint, int val){
aint.update(1, 1, n, val, {-1, -decode[val]});
}
ll dp[1 + nmax], sol[1 + nmax];
ll extract(int start, int stop, SegmentTree &aint){
return aint.query(1, 1, n, k) - (v[stop].first - v[start].first) * 2;
}
void eval(int pos, int x, int y, SegmentTree &aint){
dp[pos] = -inf;
sol[pos] = n;
x = max(pos, x);
for(int i = x; i <= y; i++){
_insert(aint, v[i].second);
ll result = extract(pos, i, aint);
if(dp[pos] < result){
dp[pos] = result;
sol[pos] = i;
}
}
for(int i = x; i <= y; i++)
_erase(aint, v[i].second);
}
void divide(int from, int to, int x, int y, SegmentTree &aint){
if(to < from)
return ;
int mid = (from + to) / 2;
for(int i = mid; i <= min(x - 1, to); i++)
_insert(aint, v[i].second);
eval(mid, x, y, aint);
for(int i = mid; i <= min(x - 1, to); i++)
_erase(aint, v[i].second);
for(int i = mid; i <= min(to, x - 1); i++)
_insert(aint, v[i].second);
divide(from, mid - 1, x, sol[mid], aint);
for(int i = mid; i <= min(to, x - 1); i++)
_erase(aint, v[i].second);
for(int i = max(to + 1, x); i < sol[mid]; i++)
_insert(aint, v[i].second);
divide(mid + 1, to, sol[mid], y, aint);
for(int i = max(to + 1, x); i < sol[mid]; i++)
_erase(aint, v[i].second);
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
for(int i = 1;i <= n; i++)
cin >> v[i].second >> v[i].first;
sort(v + 1, v + n + 1);
normalize(n);
SegmentTree aint(n);
divide(1, n, 1, n, aint);
ll result = -inf;
for(int i = 1;i <= n; i++)
result = max(result, dp[i]);
cout << result;
return 0;
}
