#include<fstream>
using namespace std;
const int N=100000;
int d[N],v[N],n,k,st=1,dr=0,dep,x[N];
long long s;
ifstream in("branza.in");
ofstream out("branza.out");
inline void stanga(int i)
{
	if(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()
{
	int i;
	in>>n>>dep>>k;
	++k;
	for(i=1;i<=n;++i)
		in>>v[i]>>x[i];
	for(i=1;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		s+=(long long)(v[d[st]]+(long long)(i-d[st])*dep)*x[i];
	}
	out<<s<<"\n";
	return 0;
}