#include<bits/stdc++.h>
#define ll long long
#define pll pair<ll, ll>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ld long double
#define sz(a) ((ll)(a).size())
using namespace std;
const ll maxn=200005, inf=1e18;
ll n, m, v[maxn], c[maxn], p[maxn], lptr=1, rptr=0, ans=-inf;
namespace SegTree
{
struct Node
{
ll cnt=0, sum=0;
Node(){}
Node(ll x): cnt(!!x), sum(x){}
};
Node St[maxn*4];
void update(ll i, ll Start, ll End, ll idx, ll val)
{
if (Start>idx || End<idx) return;
if (Start==End) {St[i]=Node(val); return;}
ll mid=(Start+End)/2;
if (mid>=idx) update(i*2, Start, mid, idx, val);
else update(i*2+1, mid+1, End, idx, val);
St[i].cnt=St[i*2].cnt+St[i*2+1].cnt;
St[i].sum=St[i*2].sum+St[i*2+1].sum;
}
void update(ll idx, ll val){update(1, 1, n, idx, val);}
ll query(ll i, ll Start, ll End, ll k)
{
if (Start==End)
{
if (!St[i].cnt) return -inf;
return St[i].sum;
}
ll mid=(Start+End)/2;
if (St[i*2+1].cnt>=k) return query(i*2+1, mid+1, End, k);
return query(i*2, Start, mid, k-St[i*2+1].cnt)+St[i*2+1].sum;
}
ll query() {return query(1, 1, n, m);}
}
ll query(ll l, ll r)
{
while (l<lptr) lptr--, SegTree::update(p[lptr], v[lptr]);
while (r>rptr) rptr++, SegTree::update(p[rptr], v[rptr]);
while (l>lptr) SegTree::update(p[lptr], 0), lptr++;
while (r<rptr) SegTree::update(p[rptr], 0), rptr--;
ll res=SegTree::query()-c[r]+c[l];
ans=max(ans, res);
return res;
}
void DnC(ll l, ll r, ll optl, ll optr)
{
if (l>r) return;
ll mid=(l+r)/2, res=0, opt=optl;
for (ll i=optl; i<=optr && i<=mid-m+1; i++)
tie(res, opt)=max(mp(res, opt), mp(query(i, mid), i));
DnC(l, mid-1, 1, n), DnC(mid+1, r, 1, n);
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> n >> m;
for (ll i=1; i<=n; i++)
cin >> v[i] >> c[i], c[i]=c[i]*2;
//sort
{
vector <pll> num;
for (ll i=1; i<=n; i++) num.pb({c[i], v[i]});
sort(num.begin(), num.end());
for (ll i=0; i<sz(num); i++) tie(c[i+1], v[i+1])=num[i];
num.clear();
for (ll i=1; i<=n; i++) num.pb({v[i], i});
sort(num.begin(), num.end());
for (ll i=0; i<sz(num); i++) p[num[i].se]=i+1;
}
DnC(1, n, 1, n), cout << ans;
}
