#include <bits/stdc++.h>
using namespace std;
const long long Nfact = 200005;
const long long mod = 1000000007;
const long long Nsieve = 1000005;
vector<bool> is_prime(Nsieve, true);
void sieve() {
  is_prime[0] = is_prime[1] = false;
  for (long long i = 2; i * i <= Nsieve; i++) {
    if (is_prime[i]) {
      for (long long j = i * i; j <= Nsieve; j += i) is_prime[j] = false;
    }
  }
}
long long bSearch(long long l, long long r, long long x,
                  vector<long long> arr) {
  while (l <= r) {
    long long m = l + (r - l) / 2;
    if (arr[m] == x) return m;
    if (arr[m] < x)
      l = m + 1;
    else
      r = m - 1;
  }
  return -1;
}
void primeFactors(long long n) {
  while (n % 2 == 0) {
    n = n / 2;
  }
  for (long long i = 3; i <= sqrt(n); i += 2) {
    while (n % i == 0) {
      n = n / i;
    }
  }
  if (n > 2) cout << n << " ";
}
long long power(long long x, long long y, long long p) {
  long long res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
long long modulo(long long a, long long b) {
  long long c = a % b;
  return (c < 0) ? c + b : c;
}
long long mul(long long x, long long y) { return (x * y) % mod; }
long long inv(long long x) { return power(x, mod - 2, mod); }
long long divide(long long x, long long y) { return mul(x, inv(y)); }
long long fact[Nfact];
void precalc() {
  fact[0] = 1;
  for (long long i = 1; i < Nfact; i++) fact[i] = mul(fact[i - 1], i);
}
long long nCr(long long n, long long k) {
  if (n < k) return 0;
  return divide(fact[n], mul(fact[k], fact[n - k]));
}
void solve() {
  long long n, k;
  cin >> n >> k;
  pair<long long, long long> p[300005];
  for (long long i = 0; i < n; i++) {
    cin >> p[i].second >> p[i].first;
  }
  sort(p, p + n);
  set<pair<long long, long long> > s;
  long long sum = 0, maxa = INT_MIN;
  for (long long i = n - 1; i >= 0; i--) {
    sum += p[i].second;
    s.insert({p[i].second, i});
    if ((long long)s.size() > k) {
      auto it = s.begin();
      sum -= it->first;
      s.erase(it);
    }
    maxa = max(maxa, p[i].first * sum);
  }
  cout << maxa << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long t = 1;
  while (t--) {
    solve();
  }
  cerr << "time taken : " << (float)clock() / CLOCKS_PER_SEC << " secs"
       << "\n";
  return 0;
}
