#include<bits/stdc++.h>
using namespace std;

const int _ = 1e5 + 9;
long long n, m;
long long a[_], b[_], flg[_];
long long tot, ans1, ans2, pos;
int main()
{
	freopen("remake.in", "r", stdin);
	freopen("remake.out", "w", stdout);
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin >> n >> m;
	for(int i = 1;i <= n;i++)
	{
		cin >> a[i] >> b[i];
		if(a[i] > 0)
			tot += (m - 1) * a[i];
		else if(b[i] >= (m - 1) * a[i])
			tot += b[i], flg[i] = 1;
		else
			tot += (m - 1) * a[i];
		if(tot > ans1)
			ans1 = tot, pos = i;
	}
	for(int i = pos + 1;i <= n;i++)
		flg[i] = 0;
	tot = 0;
	for(int i = 1;i <= n;i++)
	{
		if(a[i] > 0)
			tot += max(a[i], b[i]);
		else if(flg[i])
			tot += 0;
		else
			tot += max(a[i], b[i]);
		ans2 = max(ans2, tot);
	}
	cout << ans1 + ans2;
	
	return 0;
}