#include <bits/stdc++.h>
using namespace std;
const long long INF = (long long)1e11 + 1;
const long long mod = (long long)998244353;
const long long hell = (long long)1000000007;
long long int power(long long int x, long long int y) {
  long long int res = 1;
  while (y > 0) {
    if (y % 2) res = (x % hell * res % hell) % hell;
    x = (x % hell * x % hell) % hell;
    y = y / 2;
  }
  return res % hell;
}
long long int modinv(long long int x) { return power(x, hell - 2); }
long long int gcd(long long int a, long long int b) {
  while (b != 0) {
    long long int t = b;
    b = a % t;
    a = t;
  }
  return a;
}
void fastIO() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
class comp {
 public:
  bool operator()(pair<long long int, long long int>& a,
                  pair<long long int, long long int>& b) {
    return a.first > b.first;
  }
};
bool comp2(pair<long long int, long long int>& a,
           pair<long long int, long long int>& b) {
  return a.second > b.second;
}
void solve() {
  long long int n, k;
  cin >> n >> k;
  vector<pair<long long int, long long int>> vec(n);
  for (int i = 0; i < n; i++) cin >> vec[i].first >> vec[i].second;
  long long int ans = 0;
  for (int i = 0; i < n; i++) {
    ans = max(ans, vec[i].first * vec[i].second);
  }
  priority_queue<pair<long long int, long long int>,
                 vector<pair<long long int, long long int>>, comp>
      pq;
  sort((vec).begin(), (vec).end(), comp2);
  long long int sum = 0;
  for (int i = 0; i < n; i++) {
    sum += vec[i].first;
    if (i < k - 1) {
      ans = max(ans, sum * vec[i].second);
    } else {
      if (i >= k) {
        sum -= pq.top().first;
        pq.pop();
      }
      ans = max(ans, sum * vec[i].second);
    }
    pq.push(make_pair(vec[i].first, vec[i].second));
  }
  cout << ans;
}
int main() {
  fastIO();
  int test;
  test = 1;
  while (test--) solve();
}
