#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
const int mod=998244353;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a,bool upp=0){if(a) cout<<(upp?"YES\n":"Yes\n"); else cout<<(upp?"NO\n":"No\n");}
template<class T> void vec_out(vector<T> &p,int ty=0){
if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){assert(!a.empty());T ans=a[0]-a[0];for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}

namespace po167{
//F={a_ix + b_i}
//add ax+b in F
//return min(f(x) (in F))
//add a is strictly decrease
//need a <= 1e9, b <= 1e18
struct Convex_Hull_Trick_Weak{
	void add_Lfunction(long long a,long long b){
		while(size>1){
			if(a==A[size-1]&&B[size-1]>b){
				size--;
				continue;
			}if(a==A[size-1]&&B[size-1]<=b) return ;
			long long X=B[size-1]-B[size-2];
			long long Y=A[size-1]-a;
			long long Z=b-B[size-1];
			long long W=A[size-2]-A[size-1];
			if(X<=0&&0<=Z) break;
			if(X>=0&&0>=Z){
				size--;
				continue;
			}
			if(X/W<=Z/Y){
				if(X/W<Z/Y) break;
				if(Y*(X%W)<=W*(Z%Y)) break;
			}
			//if((B[size-1]-B[size-2])*(A[size-1]-a)<=(b-B[size-1])*(A[size-2]-A[size-1])) break;
			size--;
		}
		if(size==(int)A.size()) A.push_back(0),B.push_back(0);
		A[size]=a;
		B[size]=b;
		size++;
	}
	long long min_f(long long x){
		assert(size!=0);
		int l=-1,r=size-1;
		while(r-l>1){
			int med=(l+r)/2;
			if(A[med]*x+B[med]<A[med+1]*x+B[med+1]){
				r=med;
			}else l=med;
		}
		return A[r]*x+B[r];
	}
	private:
	std::vector<long long> A;
	std::vector<long long> B;
	int size=0;
};
}
using po167::Convex_Hull_Trick_Weak;


void solve();
// oddloop
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t=1;
    //cin>>t;
    rep(i,0,t) solve();
}

void solve(){
    ll N,M;
    cin>>N>>M;
    vector<ll> A(N),D(N);
    priority_queue<pair<ll,int>> pq;
    auto f=[&](int ind,ll len) -> ll {
        return (len*(len-1)/2)*D[ind]+len*A[ind];
    };
    rep(i,0,N){
        cin>>A[i]>>D[i];
        if(D[i]<=0) pq.push({A[i],i});
    }
    ll ans=-ILL;
    if(pq.empty()){
        rep(i,0,N){
            chmax(ans,f(i,M));
        }
        cout<<ans<<"\n";
        return;
    }
    vector<ll> p(M+1);
    rep(i,0,M){
        auto tmp=pq.top();
        pq.pop();
        p[i+1]=p[i]+tmp.first;
        tmp.first+=D[tmp.second];
        pq.push(tmp);
    }
    vector<pair<ll,ll>> q;
    rep(i,0,N){
        if(D[i]>0) q.push_back({D[i],A[i]*2ll-D[i]});
    }
    if(q.empty()){
        cout<<p[M]<<"\n";
        return;
    }
    So(q);
    Convex_Hull_Trick_Weak C;
    for(auto x:q) C.add_Lfunction(-x.first,-x.second);
    rep(i,0,M+1){
        auto tmp=C.min_f(i);
        tmp*=-i;
        tmp/=2;
        chmax(ans,tmp+p[M-i]);
        //cout<<i<<" "<<tmp<<" "<<p[M-i]<<endl;
    }
    cout<<ans<<"\n";
}