#include<stdio.h>
const int N=100001;
int x[N],d[N],v[N],n,k,st,dr=-1,i,dep;
long long s;

inline void stanga(int i)
{
	if (st<=dr && i-d[st]==k)
		++st;
}

inline void dreapta(int i)
{
	while(st<=dr && v[d[dr]]+(long long)(i-d[dr])*dep>=v[i])
		--dr;
}

inline void adauga(int i)
{
	d[++dr]=i;
}
int main()
{
	freopen("branza.in","r",stdin);
	freopen("branza.out","w",stdout);
	scanf("%d%d%d",&n,&dep,&k);
	++k;
	for(i=1;i<=n;++i)
		scanf("%d%d",&v[i],&x[i]);
	for(i=1;i<=k;++i)
	{
		dreapta(i);
		adauga(i);
		s+=(long long)(v[d[st]]+(i-d[st])*dep)*x[i];
	}
	for(;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		s+=(long long)(v[d[st]]+(i-d[st])*dep)*x[i];
	}
	printf("%lld\n",s);
}