#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001
/**
 * Author: Simon Lindholm
 * Date: 2017-04-20
 * License: CC0
 * Source: own work
 * Description: Container where you can add lines of the form kx+m, and query maximum values at points x.
 *  Useful for dynamic programming (``convex hull trick'').
 * Time: O(\log N)
 * Status: stress-tested
 */
#pragma once
using ll = long long;
struct Line {
	mutable ll k, m, p;
	bool operator<(const Line& o) const { return k < o.k; }
	bool operator<(ll x) const { return p < x; }
};

struct LineContainer : multiset<Line, less<>> {
	// (for doubles, use inf = 1/.0, div(a,b) = a/b)
	static const ll inf = LLONG_MAX;
	ll div(ll a, ll b) { // floored division
		return a / b - ((a ^ b) < 0 && a % b); }
	bool isect(iterator x, iterator y) {
		if (y == end()) return x->p = inf, 0;
		if (x->k == y->k) x->p = x->m > y->m ? inf : -inf;
		else x->p = div(y->m - x->m, x->k - y->k);
		return x->p >= y->p;
	}
	void add(ll k, ll m) {
		auto z = insert({k, m, 0}), y = z++, x = y;
		while (isect(y, z)) z = erase(z);
		if (x != begin() && isect(--x, y)) isect(x, y = erase(y));
		while ((y = x) != begin() && (--x)->p >= y->p)
			isect(x, erase(y));
	}
	ll query(ll x) {
		assert(!empty());
		auto l = *lower_bound(x);
		return l.k * x + l.m;
	}
};
int main(){
	
	int N,M;
	cin>>N>>M;
	
	LineContainer L;bool f = false;
	priority_queue<pair<long long,long long>> Q;
	rep(i,N){
		long long a,d;
		cin>>a>>d;
		if(d<0){
			Q.emplace(a,d);
		}
		else{
			L.add(d,a*2-d);
			f = true;
		}
		
	}
	long long ans = -Inf64;
	long long sum = 0;
	rep(i,M+1){
		if(i==M){
			ans = max(ans,sum);
		}
		else if(f){
			long long tt = L.query(M-i);
			tt *= M-i;
			tt /= 2;
			ans = max(ans,sum + tt);
		}
		if(Q.size()==0)break;
		if(i!=M){
			auto p = Q.top();
			Q.pop();
			sum += p.first;
			p.first += p.second;
			Q.push(p);
		}
	}
	cout<<ans<<endl;
	
	return 0;
}