#include<fstream.h>
#include<algorithm>

using namespace std;

struct vector { long long a,b ;} v[100005];

long long n,H,u,k,smax;

inline int cmp (const vector &v1, const vector &v2) { return v1.a>=v2.a; }

void afisare ()
{
	ofstream g("gutui.out");
	g<<smax;
	g.close();
}

void dinamic ()
{
	int nr,i,max=0;
	for (i=1;i<=n;i++)
		if ((H-v[i].a)/u+1>k)
		{
			smax+=max;
			k++;
			max=v[i].b;
		}
		else
			if (max<v[i].b)
				max=v[i].b;
	smax+=max;
}

void citire ()
{
	int i;
	ifstream f("gutui.in");
	f>>n>>H>>u;
	for (i=1;i<=n;i++)
		f>>v[i].a>>v[i].b;
	f.close();
}

int main()
{
	citire ();
	sort (v+1,v+n+1,cmp);
	dinamic ();
	afisare ();
	return 0;
}