#include <cstdio>

int n,s,t;
int cost[100001],cap[100001];
long long cos=0,nr;

void citire()
{
	scanf("%d %d %d",&n,&s,&t);
	for(int i=1;i<=n;i++)
		scanf("%d %d",&cost[i],&cap[i]);
}
void calcul()
{
	int i,j;
	for(i=1;i<=n;i++)
	{
		nr=cost[i];
		for(j=i;j>=i-t && j>=1;j--)
			if(cost[j]+(i-j)*s<nr)
				nr=cost[j]+(i-j)*s;
		cos=cos+nr*cap[i];
				
	}

		
}
int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	citire();
	calcul();
	printf("%d",cos);
}