#include<stdio.h>
int c[100010],m[100010],n,p[100010],s,t;

void read()
{	scanf("%d%d%d",&n,&s,&t);
	for(int i=1;i<=n;i++)
	{	scanf("%d",&c[i]);
		scanf("%d",&p[i]);
	}
}

 

void solve()
{	
	for(int i=1;i<=n;i++)
	{	int min=c[i]*p[i];
		for(int j=1;j<=t;j++)
		{	if(i-j>=1)
				if(min>c[i-j]*p[i]+j*s*p[i])
					min=c[i-j]*p[i]+j*s*p[i];
		}
		m[i]=m[i-1]+min;
		
	}
}

void write()
{
	printf("%d",m[n]);
}

int main ()
{	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	read();
	solve();
	write();
	
	
return 0;
}