#include <iostream>
#include <fstream>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
const int N=100001;
int c[N],p[N],d[101],n,t,s,sum,st=1,dr,k;
void citire()
{
    in>>n>>s>>t;
    for(int i=1;i<=n;i++)
        in>>c[i]>>p[i];
}
void stanga(int i)
{
    if(i-d[st] == t)
        st++;
}
void dreapta(int i)
{
    while(st<=dr && c[i]<=c[d[dr]]+s*k)
    {
        dr--;
        k++;
    }
    if(st>dr)
        k=0;

}
int main()
{
    citire();
    for(int i=1;i<=n;i++)
    {
        k=1;
        if(i>t || c[i]<=c[d[dr]]+s*k)
            stanga(i);
        dreapta(i);
        d[++dr]=i;
        //if(i>=t)
        sum+=(c[d[st]]+s*k)*p[i];
    }
    out<<sum;
    return 0;
}