#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int N, M;
cin >> N >> M;
vector<pair<ll,ll>> a(N);
for (int i = 0; i < N; ++i)
cin >> a[i].first >> a[i].second; // V, C
sort(a.begin(), a.end(), [](auto &x, auto &y){ return x.second < y.second; });
vector<ll> pref(N+1, 0);
for (int i = 0; i < N; ++i) pref[i+1] = pref[i] + a[i].first;
vector<ll> gap(N-1);
for (int i = 0; i < N-1; ++i) gap[i] = a[i+1].second - a[i].second;
// Sparse table for range maximum on gaps
int LOG = 20;
vector<vector<ll>> st(LOG, vector<ll>(N-1));
st[0] = gap;
for (int k = 1; (1 << k) <= N-1; ++k)
for (int i = 0; i + (1 << k) <= N-1; ++i)
st[k][i] = max(st[k-1][i], st[k-1][i + (1 << (k-1))]);
auto range_max = [&](int l, int r) {
if (l > r) return 0LL;
int len = r - l + 1;
int k = __lg(len);
return max(st[k][l], st[k][r - (1 << k) + 1]);
};
ll ans = LLONG_MIN;
for (int i = 0; i + M <= N; ++i) {
ll sumV = pref[i+M] - pref[i];
ll range = a[i+M-1].second - a[i].second;
ll largest_gap = range_max(i, i+M-2);
ll beauty = sumV - 2 * range + largest_gap;
ans = max(ans, beauty);
}
cout << ans << "\n";
return 0;
}
