#include <bits/stdc++.h>
using namespace std;
using ll = long long ;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T l, T r) { while (l != r) cerr << *l << " \n"[next(l) == r], ++l; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 300010, inf = 1e9 + 10, MAX_M = 2010;
const ll linf = 1ll << 59;
int n, k;
// color, value
pair<int,int> cake[MAX_N];
ll dp[MAX_M][MAX_M];
int32_t main() {
ios_base::sync_with_stdio(0), cin.tie(0);
cin >> n >> k;
for (int i = 1;i <= n;++i) {
auto &[c, v] = cake[i];
cin >> v >> c;
}
sort(cake+1, cake+1 + n);
if (n > 2000) return -1;
for (int i = 0;i <= n;++i)
for (int j = 0;j <= k;++j)
dp[i][j] = -linf;
ll res = -linf;
for (int i = 1;i <= n;++i) {
auto [c, v] = cake[i];
chmax(res, dp[i-1][k-1] + v - 2 * c);
for (int j = 1;j <= k;++j) {
chmax(dp[i][j], max(dp[i-1][j], dp[i-1][j-1] + v));
}
chmax(dp[i][1], v + 2ll * c);
}
cout << res << '\n';
}
