#include <stdio.h>

long long n,s,t,c[100010],p[100010],d[100010],a[100010],st,fi,sol;
int i,j;

int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	scanf("%lld%lld%lld",&n,&s,&t);
	for (i=1; i<=n; ++i) scanf("%lld%lld",&c[i],&p[i]);
	d[1]=c[1];
	a[1]=1;
	st=1; fi=1;
	sol=d[1]*p[1];
	for (i=2; i<=n; ++i)
	{
		if (t<i-a[st]) ++st;
		while (fi>=st && c[i]<=c[a[fi]]+(i-a[fi])*s) --fi;
		a[++fi]=i;
		d[i]=c[a[st]]+(i-a[st])*s;
		sol+=d[i]*p[i];
	}
	printf("%lld\n",sol);
	return 0;
}