#include <bits/stdc++.h>
#define int long long
//#pragma GCC optimize("Ofast")
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
#define file(s) freopen(s".in","r",stdin); freopen(s".out","w",stdout);
#define forev(i, b, a) for(int i = (b); i >= (a); --i)
#define forn(i, a, b) for(int i = (a); i <= (b); ++i)
#define all(x) x.begin(), x.end()
#define sz(s) (int)s.size()
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define s second
#define f first
using namespace std;
typedef pair < long long, long long > pll;
typedef pair < int, int > pii;
typedef unsigned long long ull;
typedef vector < pii > vpii;
typedef vector < int > vi;
typedef long double ldb;
typedef long long ll;
typedef double db;
const int inf = 1e9, maxn = 4e5 + 148, mod = 1e9 + 7, N = 2e3 + 11;
const int dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1}, block = 333;
const pii base = mp(1171, 3307), Mod = mp(1e9 + 7, 1e9 + 9);
const db eps = 1e-12, pi = 3.14159265359;
const ll INF = 1e18;
vi x;
int n, m, b[N];
pii a[N], t[N << 2];
void update (int pos, int x, int v = 1, int tl = 0, int tr = n - 1) {
if (tl == tr) {
t[v].f += x;
++t[v].s;
return;
}
int tm = (tl + tr) / 2;
if (pos <= tm)
update(pos, x, v << 1, tl, tm);
else
update(pos, x, v << 1 | 1, tm + 1, tr);
t[v].f = t[v << 1].f + t[v << 1 | 1].f;
t[v].s = t[v << 1].s + t[v << 1 | 1].s;
}
void build (int v = 1, int tl = 0, int tr = n - 1) {
t[v] = {0, 0};
if (tl == tr)
return;
int tm = (tl + tr) / 2;
build(v << 1, tl, tm);
build(v << 1 | 1, tm + 1, tr);
}
int get (int k, int v = 1) {
if (!k)
return 0;
cerr << k << ' ' << v << ' ' << t[v].s << endl;
if (t[v].s == k)
return t[v].f;
if (t[v << 1].s > k)
return get(k, v << 1);
return t[v << 1].f + get(k - t[v << 1].s, v << 1 | 1);
}
main () {
cin >> n >> m;
for (int i = 1; i <= n; ++i) {
cin >> a[i].s >> a[i].f;
x.pb(a[i].s);
}
sort(all(x));
sort(a + 1, a + 1 + n);
for (int i = 1; i <= n; ++i)
b[i] = sz(x) - 1 - (lower_bound(all(x), a[i].s) - x.begin());
int ans = -INF;
for (int i = 1; i <= n; ++i) {
build();
for (int j = i + 1; j <= n; ++j) {
if (t[1].s >= m - 2)
ans = max(ans, a[i].s + a[j].s - 2*(a[j].f - a[i].f) + get(m - 2));
update(b[j], a[j].s);
}
}
cout << ans << endl;
}
