#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <atcoder/modint>
using namespace std;
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(i64 i=0; i<(i64)(n); i++)
#define repr(i,n) for(i64 i=(i64)(n)-1; i>=0; i--)
const i64 INF = 4001001001001001001;
using Modint = atcoder::static_modint<998244353>;

struct LiChaoTree{
  using Val = i64;
  struct Func {
    i64 a, b;
    Val operator()(i64 x) { return a * x + b; }
  };
  static Func infFunc() { return { 0,INF }; }
 
  int N;
  vector<Func> V;
  vector<bool> visited;
  
  LiChaoTree(i64 n){
    N = 1;
    while(N < n) N *= 2;
    V.assign(N*2, infFunc());
    visited.assign(N*2, false);
  }
 
  void addSegment(i64 l, i64 r, Func f){
    if(l >= r) return;
    auto dfs = [&,this](int i,Func f,i64 a,i64 b,auto dfs) -> void {
      visited[i] = true;
      if(i >= V.size()) return;
      if(r <= a || b <= l) return;
      i64 m = (a+b)/2;
      if(!(l <= a && b <= r)){
        dfs(i*2,f,a,m,dfs);
        dfs(i*2+1,f,m,b,dfs);
        return;
      }
      bool greatf_l = !(V[i](a) < f(a));
      bool greatf_r = !(V[i](b-1) < f(b-1));
      if(!greatf_l && !greatf_r) return;
      if(greatf_l && greatf_r){ V[i] = f; return; }
      if(a + 1 == b) return;
      if(!(V[i](m) < f(m))){
        swap(V[i],f);
        swap(greatf_l,greatf_r);
      }
      if(greatf_l) dfs(i*2,f,a,m,dfs);
      else dfs(i*2+1,f,m,b,dfs);
    };
    dfs(1,f,0,N,dfs);
  }
  
  void addLine(Func f){
    addSegment(0,N,f);
  }
 
  Val minVal(i64 p){
    int i = 1;
    Val res = infFunc()(p);
    int l = 0, r = N;
    while(i < V.size()){
      if(!visited[i]) break;
      res = min(res,V[i](p));
      i64 m = (l+r)/2;
      if(p < m){ i = i*2; r = m; }
      else{ i = i*2+1; l = m; }
    }
    return res;
  }
 
  Func minFunc(i64 p){
    int i = 1;
    Func res = infFunc();
    int l = 0, r = N;
    while(i < V.size()){
      if(!visited[i]) break;
      if(V[i](p) < res(p)) res = V[i];
      i64 m = (l+r)/2;
      if(p < m){ i = i*2; r = m; }
      else{ i = i*2+1; l = m; }
    }
    return res;
  }
};


int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    i64 N, M; cin >> N >> M;
    vector<pair<i64, i64>> A, B;
    rep(i,N){
        i64 a,d; cin >> a >> d;
        if(d <= 0) B.push_back({ d, a });
        else A.push_back({ d, a });
    }
    auto nthTerm = [](i64 d, i64 a, i64 n) -> i64 {
        return a + d * n;
    };
    auto prefixSum = [](i64 d, i64 a, i64 n) -> i64 {
        i64 ans = a * n;
        ans += d * ((n*n-n)/2);
        return ans;
    };
    vector<i64> valdown;
    {
        int n = B.size();
        vector<int> ptr(n);
        priority_queue<pair<i64, i64>> que;
        rep(v,n){
            auto [d,a] = B[v];
            que.push({ nthTerm(d, a, ptr[v]), v });
        }
        rep(i,M){
            auto [p,v] = que.top(); que.pop();
            valdown.push_back(p);
            ptr[v]++;
            auto [d,a] = B[v];
            que.push({ nthTerm(d, a, ptr[v]), v });
        }
    }
    vector<i64> valup(M+1);
    if(!A.empty()) {
        LiChaoTree ds(M+1);
        for(auto [d,a] : A){
            LiChaoTree::Func f;
            f.a = -d; f.b = -2*a+d;
            ds.addLine(f);
        }
        for(int i=0; i<=M; i++){
            i64 q = -ds.minVal(i);
            valup[i] = q * i / 2;
        }
    } else {
        rep(i,M) valup[i+1] = -INF;
    }
    vector<i64> valdownSum(M+1);
    rep(i,M) valdownSum[i+1] = valdownSum[i] + valdown[i];
    i64 ans = -INF;
    rep(i,M+1) ans = max(ans, valdownSum[i] + valup[M-i]);
    cout << ans << endl;
    return 0;
}