#include <stdio.h>

int n,s,t,i,j,c[6],p[6],d[6],a[6],st,fi,sol;

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