#include <stdio.h>

long long v[100001],p[100001];
long long s;

int main()
{
	long long n,k,i,c=0,j,x,l=1,t,y,a;
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	scanf("%lld%lld%lld",&n,&a,&t);
	v[1]=10000001;
	for (i=1;i<t+1;i++)
	{
		scanf("%lld%lld",&x,&y);
		++c;
		while ((x<v[c-1]+(i-p[c-1])*a)&&(c>1)) {--c;}
		v[c]=x;p[c]=i;s+=(v[l]+(i-p[l])*a)*y;
	}
	for (i=i;i<n+1;i++)
	{
		if (p[l]==i-t) ++l;
		scanf("%lld%lld",&x,&y);
		++c;
		while ((x<v[c-1]+(i-p[c-1])*a)&&(c>l)) {--c;}
		v[c]=x;p[c]=i;s+=(v[l]+(i-p[l])*a)*y;
	}
	printf("%lld",s);
	return 0;
}