#include <iostream>
#include <fstream>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");
const int N=100010;
long long n,s,t,d[N],st,dr;
long long cost_min,p[N],c[N];
struct brnz
{
    long long p,c;
}v[N];
int main()
{
    f>>n>>s>>t;
    st=0;
    dr=-1;
    cost_min=0;
    for(int i=0; i<n; i++)
        f>>v[i].p>>v[i].c;
    for(int i=0; i<n; i++)
    {
        if(st<=dr && d[st]==i-t)
        {
            st++;
        }
        while(st<=dr && v[i].p<=v[d[dr]].p+s*(i-d[dr]))
        {
            dr--;
        }
        d[++dr]=i;
       cost_min+=(long long)v[i].c*(v[d[st]].p+ s*(i-d[st]));

    }
    g<<cost_min;
    return 0;
}