#include<stdio.h>
struct Dq{
	long long p,c;
	int cp;
};
Dq deque[100000];
Dq aux;
int st,end;
int n,t,s,ft,cop;
long long sum;
void add(Dq a);
int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	scanf("%d%d%d",&n,&s,&t);
	for(int i=1;i<=n;++i)
	{
		
		scanf("%d%d",&aux.c,&aux.p);
		
		cop=aux.p;
		aux.p=i;
		
		add(aux);
		
		if(deque[st].p>t)
			++st;
		
		sum+=deque[st].c*deque[st].cp;
		
	}
	printf("%lld",sum);
	return 0;
}
void add(Dq a)
{
	int i;
	i=st;
	if(ft)
	{
	while(a.c>deque[i].c+s&&deque[i].c)
		{
			//deque[i].p++;
			deque[i].c+=s;
			deque[i].cp=cop;
			++i;
		}
	}
	ft=1;
	deque[i].p=aux.p;
	deque[i].c=aux.c;
	deque[i].cp=cop;
	end=i;
}