#include <stdio.h>
#define NMAX 100001
#define INF 1000000000
#define ll long long
int n,s,t,A[NMAX],B[NMAX],C[NMAX];
ll rez;
void read()
{
	scanf("%d%d%d",&n,&s,&t);
	int i;
	for (i=1; i<=n; i++)
		scanf("%d%d",&A[i],&B[i]);
}
inline int min(int x,int y)
{
	return x<y ? x : y;
}
void solve()
{
	int i,j;
	for (i=1; i<=n; i++)
	{
		C[i]=INF;
		for (j=i; j>=i-t && j>=1; j--)
			C[i]=min(C[i],A[j]+(i-j)*s);
		rez+=(ll)C[i]*B[i];
	}
}
int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	read();
	solve();
	printf("%lld\n",rez);
	return 0;
}