#include<fstream>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
const int N = 100005;
int v[N],p[N],n,s,t,dq[N],st=1,dr,r;
void noapte(){
	int i;
	for(i=st;i<=dr;i++) v[dq[i]]+=s;
}
void stanga(int i){
	if(i-dq[st]==t) st++;
}
void dreapta(int i){
	while(dr>=st && v[i]<=v[dq[dr]]) dr--;
}
int main(){
	int i;
	in>>n>>s>>t;
	for(i=1;i<=n;i++) in>>v[i]>>p[i];
	for(i=1;i<=n;i++){
		if(i>=t) stanga(i);
		noapte();
		dreapta(i);
		dq[++dr]=i;
		//for(int j=st;j<=dr;j++) out<<v[dq[j]]<<' '; out<<'\n';
		r+=v[dq[st]]*p[i];
	}
	out<<r;
	return 0;
}