#include <fstream>
#include <algorithm>

using namespace std;
struct lol
{
	int a,b;
}v[100005];
int cmp(lol x ,lol y)
{
	return x.a<y.a;
}
int main()
{
	ifstream cin("lupu.in");
	ofstream cout("lupu.out");

	int n,l,x,a,b,s=0,h=0,m=0;
	cin>>n>>x>>l;

	for(int i=0;i<n;i++)
	{
		cin>>v[i].a>>v[i].b;
	}
	sort(v,v+n,cmp);

    for(int i=0;i<=x;i+=l)
	{
		while(h<n && v[h].a<=i)
		{
			m=max(m, v[h].b);
			h++;
		}
		s+=m;
		m=0;
	}

	cout<<s;

    return 0;
}