#pragma GCC optimize("O2")
#include <algorithm>
#include <array>
#include <bit>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfenv>
#include <cfloat>
#include <chrono>
#include <cinttypes>
#include <climits>
#include <cmath>
#include <compare>
#include <complex>
#include <concepts>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <initializer_list>
#include <iomanip>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <new>
#include <numbers>
#include <numeric>
#include <ostream>
#include <queue>
#include <random>
#include <ranges>
#include <set>
#include <span>
#include <sstream>
#include <stack>
#include <streambuf>
#include <string>
#include <tuple>
#include <type_traits>
#include <variant>

#define int ll
#define INT128_MAX (__int128)(((unsigned __int128) 1 << ((sizeof(__int128) * __CHAR_BIT__) - 1)) - 1)
#define INT128_MIN (-INT128_MAX - 1)

namespace R = std::ranges;
namespace V = std::views;

using namespace std;

using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<long long, long long>;
using tiii = tuple<int, int, int>;
using ldb = long double;
//#define double ldb

template<class T>
ostream& operator<<(ostream& os, const pair<T, T> pr) {
  return os << pr.first << ' ' << pr.second;
}
template<class T, size_t N>
ostream& operator<<(ostream& os, const array<T, N> &arr) {
  for(const T &X : arr)
    os << X << ' ';
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const vector<T> &vec) {
  for(const T &X : vec)
    os << X << ' ';
  return os;
}

using frac = array<int, 2>;
bool operator<=(frac a, frac b) {
  return a[0] * b[1] <= a[1] * b[0];
}

frac inter(frac a, frac b) {
  if (a[0] > b[0])
    return {b[1] - a[1], a[0] - b[0]};
  else if (a[0] < b[0])
    return {a[1] - b[1], b[0] - a[0]};
  else
    assert(false);
}

signed main() {
  ios::sync_with_stdio(false), cin.tie(NULL);

  int n, m; cin >> n >> m;
  vector<int> a(n), d(n);
  for(int i = 0; i < n; i++)
    cin >> a[i] >> d[i];

  if (R::min(d) >= 0) {
    int ans = LLONG_MIN;
    for(int i = 0; i < n; i++)
      ans = max(ans, m * a[i] + m * (m - 1) / 2 * d[i]);
    cout << ans << '\n';
    return 0;
  }

  vector<int> s(1, 0);
  {
    priority_queue<array<int, 2>> pq;
    vector<int> k(n);
    for(int i = 0; i < n; i++) {
      if (d[i] < 0) {
        pq.push({a[i], i});
        k[i] = 1;
      }
    }
    for(int i = 0; i < m; i++) {
      auto [val, id] = pq.top(); pq.pop();
      s.emplace_back(val);
      pq.push({a[id] + k[id] * d[id], id});
      k[id]++;
    }
    partial_sum(s.begin(), s.end(), s.begin());
  }

  if (R::max(d) < 0) {
    cout << s[m] << '\n';
    return 0;
  }

  vector<array<int, 2>> l;
  for(int i = 0; i < n; i++)
    if (d[i] >= 0)
      l.push_back({d[i], 2 * a[i] - d[i]});
  R::sort(l);

  deque<array<int, 2>> cht;
  for(int i = 1; i <= ssize(l); i++) {
    if (i == ssize(l) or l[i - 1][0] != l[i][0]) {
      while(ssize(cht) >= 2 and inter(l[i - 1], end(cht)[-2]) <= inter(end(cht)[-2], end(cht)[-1]))
        cht.pop_back();
      cht.push_back(l[i - 1]);
    }
  }

  int ans = LLONG_MIN;
  for(int k = 0; k <= m; k++) {
    //while(ssize(cht) >= 2 and inter(cht[0], cht[1]) <= frac{k, 1})
    while(ssize(cht) >= 2 and inter(cht[0], cht[1])[0] <= inter(cht[0], cht[1])[1] * k)
      cht.pop_front();
    int eval = k * cht.front()[0] + cht.front()[1];
    ans = max(ans, eval * k / 2 + s[m - k]);
  }

  cout << ans << '\n';

  return 0;
}