#include <bits/stdc++.h>
#define in(x) freopen(x,"r",stdin)
#define out(x) freopen(x,"w",stdout)
#define F first
#define S second
#define pb push_back
#define M ll(998244353)
#define inf ll(2e9+7)
#define N ll(200500)
#define sz(x) x.size()
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#define el '\n'
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds;
//typedef tree <ll, null_type, less_equal <ll>, rb_tree_tag, tree_order_statistics_node_update> os;
multiset <pair <ll, ll> , greater <pair <ll, ll> > > se;
ll w, h, i, n, k, ans;
vector <pair <ll, ll> > v;
int main()
{
// in("input.txt");
// out("output.txt");
ios_base::sync_with_stdio(false);
iostream::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> k;
for (i = 1; i <= n; i++)
{
cin >> w >> h;
v.pb({w, h});
}
w = 0;
sort(v.begin(), v.end());
for (i = 0; i < k; i++) se.insert({v[i].S, v[i].F}), w += v[i].F, h = (*se.begin()).F;
ans = w * h;
for (i = k; i < n; i++)
{
if (v[i].S < (*se.begin()).F)
{
w -= (*se.begin()).S;
se.erase(se.begin());
w += v[i].F;
se.insert({v[i].S, v[i].F});
h = (*se.begin()).F;
ans = min(ans, w * h);
}
}
cout << ans;
}
