#include<stdio.h>
#define NMAX 101000
long long i,in,sf,j,a,poz,max,s,n,b,k,m,rez,y[NMAX];
struct deque
{
	long long I,C;
};
deque q[NMAX],aux;
struct kkt
{
	long long C,X;
};
kkt x[NMAX];
int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	scanf("%lld%lld%lld",&n,&s,&k);
	for (i=1;i<=n;i++)
		scanf("%lld%lld",&x[i].C,&x[i].X);
	in=1;
	sf=0;
	for (i=1;i<=n;i++)
	{
		while ((in<=sf&&i-q[in].I>k))
			in++;
		while (in<=sf&&q[sf].C>x[i].C+(n-i)*s)
			sf--;
		q[++sf].C=x[i].C+(n-i)*s;
		q[sf].I=i;
		y[i]=q[in].C-(n-q[in].I)*s;
	}
	for (i=1;i<=n;i++)
	{
		q[i].C=y[i];
		q[i].I=i;
	}

	a=1;
	while (a)
	{
		a=0;
		for (i=1;i<n;i++)
			if ((q[i].C>q[i+1].C)||(q[i].C==q[i+1].C&&q[i].I>q[i+1].I))
			{
				a=1;
				aux=q[i];
				q[i]=q[i+1];
				q[i+1]=aux;
			}
	}

	for (i=1;i<=n;i++)
	{
		if (q[i].C==q[i+1].C)
		{
			a=0;
			b=0;
			j=i;
			while (q[i].C==q[i+1].C)
			{
				a+=(x[q[i].I+1].X)*(q[i].I+1-q[j].I);
				b+=x[q[i].I+1].X;
				i++;
			}
			rez+=a*s;
			rez+=(b+x[q[j].I].X)*x[q[j].I].C;
		} else
		rez+=q[i].C*x[q[i].I].X;
	}


/*	for (i=1;i<=n;i++)
	{
		if (y[i]==y[i+1])
		{
			a=0;
			b=0;
			j=i;
			while (y[i]==y[i+1])
			{
				a+=(x[i+1].X)*(i+1-j);
				b+=x[i+1].X;
				i++;
			}
			rez+=a*s;
			rez+=(b+x[j].X)*x[j].C;
		} else
		rez+=y[i]*x[i].X;
	} */
	printf("%lld\n",rez);



	return 0;
}