#include<bits/stdc++.h>
using namespace std;
#define us unsigned
#define ll long long
#define db double
#define ldb long double
#define pb push_back
#define rs resize
#define il inline
#define For(i,a,b) for(ll i=(a);i<=(b);++i)
#define Rep(i,a,b) for(ll i=(a);i>=(b);--i)
//#define getchar getchar_unlocked
inline ll read(){
	ll num=0,f=1;char c=getchar();
	while(c>'9' || c<'0'){if(c=='-')f=-1;c=getchar();}
	while(c>='0' && c<='9')num=(num<<3)+(num<<1)+(c^48),c=getchar();
	return num*f;
}
inline void write(ll x){
	if(x<0)putchar('-'),x=-x;
	if(x>9)write(x/10);
	putchar(x%10^48);
}
const ll N=1e5+5;
ll n,m,a[N],b[N],ans=-1e18,f[N];
int main(){
	//ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	//freopen("remake.in","r",stdin);
	//freopen("remake.out","w",stdout);
	n=read(),m=read();
	For(i,1,n){
		a[i]=read(),b[i]=read();
	}
	For(i,1,n){
		ll res=b[i],
		res1=a[i]*m,
		res2=a[i]*(m-1)+b[i],
    res3=a[i];
		f[i]=f[i-1]+max({res,res1,res2,res3});
		ans=max(ans,f[i]);
	}
	write(ans);
	return 0;
}
//114514