#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e5+5;
struct Node{
	int a,b;
}G[N];
int sum[N],sum2[N],vis[N];
//int cmp(int a,int b){
//	return a>b;
//}
void solve(){
	int n,m,maxx=0,maxx2=0;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>G[i].a>>G[i].b;
	}
	for(int i=1;i<=n;i++){
		if(G[i].a<0){
			if(G[i].a*(m-1)<G[i].b){
				sum[i]=sum[i-1]+G[i].b;
				vis[i]=1;
				//cout<<i<<"pppppp";
			}
			else{
				sum[i]=sum[i-1]+G[i].a*(m-1);
			}
		}
		else
			sum[i]=sum[i-1]+G[i].a*(m-1);
		//cout<<sum[i]<<"\n";
		maxx=max(maxx,sum[i]);
	}
	//cout<<maxx;
	for(int i=1;i<=n;i++){
		if(vis[i]==1){
			sum2[i]=sum2[i-1];
		}
		else{
			sum2[i]=sum2[i-1]+max(G[i].a,G[i].b);
		}
		maxx2=max(maxx2,sum2[i]);
	}
	cout<<maxx+maxx2;
//	for(int i=1;i<=n;i++){
//		sum[i]=sum[i-1]+G[i].a;
//		maxx=max(maxx,sum[i]);
//		sum2[i]=sum2[i-1]+max(G[i].a,G[i].b);
//		cout<<sum[i]<<" "<<sum2[i]<<"\n";
//		maxx2=max(maxx2,sum2[i]);
//	}
//	int ans=maxx*(m-1)+maxx2;
//	cout<<ans;
}
signed main(){
	freopen("remake.in","r",stdin);
	freopen("remake.out","w",stdout);
	int T;
	T=1;
	while(T--){
		solve();
	}
}