#include <fstream>

using namespace std;
int maxx[100001];
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>>a>>b;
		if(b>maxx[a])
		{
			maxx[a]=b;
		}
	}
	for(int i=x/l;i>=0;i--)
	{
		while(h<=x && (x-h)/l>=i)
		{
			if(maxx[h]>m)
				m=maxx[h];
			h++;
		}
		s+=m;
		m=0;
	}

	cout<<s;

    return 0;
}