# pragma GCC optimize("Ofast,no-stack-protector")

# pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

# include <bits/stdc++.h>

# define I return

# define AK 0

# define IOI ;

using namespace std;

typedef long long ll;

typedef pair <int, int> pii;

int n, k, maxx[200005];

ll dp[200005][15];

pii a[200005];

bool cmp (const pii& a, const pii& b) {

	return a.first * b.second + a.second < b.first * a.second + b.second;

}

int main () {

	ios::sync_with_stdio (0);

	cin.tie (0);

	cout.tie (0);

	cin >> n >> k;

	maxx[0] = 1;

	for (int i = 1; i <= n; ++ i)
		cin >> a[i].first >> a[i].second;

	sort (a + 1, a + 1 + n, cmp);

	for (int i = 1; i <= n; ++ i)
		for (int j = k; j; -- j)
			maxx[j] = max (maxx[j], a[i].first * maxx[j - 1] + a[i].second);

	cout << maxx[k];

	I AK IOI

}