#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
clock_t t1, t2;
long long binPow(long long a, long long b) {
  long long x = 1, y = a;
  while (b) {
    if (b & 1) x = (x * y) % mod;
    y = (y * y) % mod;
    b >>= 1;
  }
  return x % mod;
}
long long inverserEuler(int n) { return binPow(n, mod - 2); }
long long C(int k, int n) {
  vector<long long> f(n + 1, 1);
  for (int i = 2; i <= n; i++) f[i] = (f[i - 1] * i) % mod;
  return (f[n] * ((inverserEuler(f[k]) * inverserEuler(f[n - k])) % mod) %
          mod) %
         mod;
}
const int maxn = 3e5;
int n, k;
vector<pair<int, int>> p(maxn);
void trunghieu() {
  cin >> n >> k;
  int i, j;
  for (i = 0; i < n; ++i) cin >> p[i].first >> p[i].second;
  sort(p.begin(), p.begin() + n, [](pair<int, int> a, pair<int, int> b) {
    return a.second > b.second || a.second == b.second && a.first > b.first;
  });
  long long ans = 0, sum = 0, minV = INT_MAX;
  for (i = 0; i < k; ++i) {
    minV = min(minV, 1LL * p[i].second);
    sum += p[i].first;
    ans = max(ans, 1LL * sum * minV);
  }
  cout << ans << endl;
}
int main() {
  cerr << "Program is running" << endl;
  t1 = clock();
  ios::sync_with_stdio(false);
  cin.tie();
  trunghieu();
  t2 = clock();
  float diff((float)t2 - (float)t1);
  float seconds = diff / CLOCKS_PER_SEC;
  cerr << "Running in " << seconds << " seconds" << endl;
  return 0;
}
