#ifndef LOCAL
#define FAST_IO
#endif

// ============
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#include <functional>

#define OVERRIDE(a, b, c, d, ...) d
#define REP2(i, n) for (i32 i = 0; i < (i32)(n); ++i)
#define REP3(i, m, n) for (i32 i = (i32)(m); i < (i32)(n); ++i)
#define REP(...) OVERRIDE(__VA_ARGS__, REP3, REP2)(__VA_ARGS__)
#define PER(i, n) for (i32 i = (i32)(n) - 1; i >= 0; --i)
#define ALL(x) begin(x), end(x)

using namespace std;

using u32 = unsigned int;
using u64 = unsigned long long;
using i32 = signed int;
using i64 = signed long long;
using f64 = double;
using f80 = long double;

template <typename T>
using Vec = vector<T>;

template <typename T>
bool chmin(T &x, const T &y) {
    if (x > y) {
        x = y;
        return true;
    }
    return false;
}
template <typename T>
bool chmax(T &x, const T &y) {
    if (x < y) {
        x = y;
        return true;
    }
    return false;
}

#ifdef INT128

using u128 = __uint128_t;
using i128 = __int128_t;

istream &operator>>(istream &is, i128 &x) {
    i64 v;
    is >> v;
    x = v;
    return is;
}
ostream &operator<<(ostream &os, i128 x) {
    os << (i64)x;
    return os;
}
istream &operator>>(istream &is, u128 &x) {
    u64 v;
    is >> v;
    x = v;
    return is;
}
ostream &operator<<(ostream &os, u128 x) {
    os << (u64)x;
    return os;
}

#endif

[[maybe_unused]] constexpr i32 INF = 1000000100;
[[maybe_unused]] constexpr i64 INF64 = 3000000000000000100;
struct SetUpIO {
    SetUpIO() {
#ifdef FAST_IO
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
#endif
        cout << fixed << setprecision(15);
    }
} set_up_io;
// ============

#ifdef DEBUGF
#else
#define DBG(x) (void) 0
#endif

// https://ei1333.github.io/library/dp/monotone-minima.hpp
template< typename T, typename Compare = less< T > >
vector< pair< int, T > > monotone_minima(int H, int W, const function< T(int, int) > &f, const Compare &comp = Compare()) {
  vector< pair< int, T > > dp(H);
  function< void(int, int, int, int) > dfs = [&](int top, int bottom, int left, int right) {
    if(top > bottom) return;
    int line = (top + bottom) / 2;
    T ma;
    int mi = -1;
    for(int i = left; i <= right; i++) {
      T cst = f(line, i);
      if(mi == -1 || comp(cst, ma)) {
        ma = cst;
        mi = i;
      }
    }
    dp[line] = make_pair(mi, ma);
    dfs(top, line - 1, left, mi);
    dfs(line + 1, bottom, mi, right);
  };
  dfs(0, H - 1, 0, W - 1);
  return dp;
}

int main() {
    i32 n, m;
    cin >> n >> m;
    Vec<i64> a(n), d(n);
    REP(i, n) {
        cin >> a[i] >> d[i];
    }
    Vec<i32> plus, minus;
    REP(i, n) {
        if (d[i] > 0) {
            plus.push_back(i);
        } else {
            minus.push_back(i);
        }
    }
    Vec<i64> pct(m + 1, -INF64);
    pct[0] = 0;
    if (!minus.empty()) {
        priority_queue<pair<i64, i32>> pq;
        Vec<i32> cnt(n, 0);
        for (i32 i : minus) {
            pq.emplace(a[i] + cnt[i] * d[i], i);
        }
        REP(i, m) {
            auto [val, idx] = pq.top();
            pq.pop();
            pct[i + 1] = pct[i] + val;
            ++cnt[idx];
            pq.emplace(a[idx] + cnt[idx] * d[idx], idx);
        }
    }
    DBG(pct);
    Vec<i64> prob(m + 1, -INF64);
    prob[0] = 0;
    if (!plus.empty()) {
        sort(ALL(plus), [&](i32 i, i32 j) -> bool {
            return d[i] < d[j];
        });
        DBG(plus);
        const auto get = [&](i32 i, i32 j) -> i64 {
            i32 idx = plus[j];
            i64 first = a[idx];
            i64 last = a[idx] + d[idx] * (i - 1);
            return (first + last) * i / 2;
        };
        auto ret = monotone_minima<i64, greater<>>(m + 1, (i32)plus.size(), get);
        REP(i, m + 1) {
            prob[i] = ret[i].second;
        }
    }
    DBG(prob);
    i64 ans = -INF64;
    REP(i, m + 1) {
        chmax(ans, pct[i] + prob[m - i]);
    }
    cout << ans << '\n';
}