#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>

using namespace std;

ifstream in("gutui.in");
ofstream out("gutui.out");

const int N=100001;

int n,height,u,offset,rez,maxg;
priority_queue< pair<int,int> > heap;


int main(){
	int i,x,y;
	in>>n>>height>>u;
	for(i=1;i<=n;++i){
		in>>x>>y;
		heap.push(make_pair(y,x));
	}
	for(i=1;i<=n;i++){
		if(heap.top().second+offset<=height){
			rez+=heap.top().first;
			offset+=u;
		}
		heap.pop();
	}
	out<<rez;
	return 0;
}