#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  ll N, M;
  cin >> N >> M;

  auto sum = [&](ll a, ll d) { return (a + a + (M - 1) * d) * M / 2; };

  vector<ll> A(N), D(N);
  for(ll i = 0; i < N; i++) { cin >> A[i] >> D[i]; }

  ll m = 0, idx = -1;
  for(ll i = 0; i < N; i++) {
    if(D[i] < 0) { continue; }
    ll tmp = sum(A[i], D[i]);
    if(tmp > m) {
      idx = i;
      m = tmp;
    }
    else if(tmp == m) {
      if(idx == -1 || D[idx] > D[i]) { idx = i; }
    }
  }

  if(idx == -1) {
    priority_queue<pair<ll, ll>> q;
    for(ll i = 0; i < N; i++) { q.emplace(A[i], D[i]); }

    ll ans = 0;
    for(ll i = 0; i < M; i++) {
      auto [t, d] = q.top();
      q.pop();
      ans += t;
      q.emplace(t + d, d);
    }
    cout << ans << "\n";
  }
  else {
    vector<ll> single;
    for(ll i = 0; i < M; i++) { single.emplace_back(A[idx] + D[idx] * i); }

    priority_queue<pair<ll, ll>> q;
    for(ll i = 0; i < N; i++) {
      if(D[i] < 0) { q.emplace(A[i], D[i]); }
    }

    ll ans = m;
    for(ll i = 0; i < M; i++) {
      auto [t, d] = q.top();
      q.pop();
      if(t > single.back()) {
        ans += t - single.back();
        single.pop_back();
        q.emplace(t + d, d);
      }
      else { break; }
    }
    cout << ans << "\n";
  }
}