#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],i,st,dr;
long long cost_min,p[N],c[N];

int main()
{
    f>>n>>s>>t;
    st=0;
    dr=-1;
    cost_min=0;
    for(i=0; i<n; i++)
    {
        f>>p[i]>>c[i];
        if(st<=dr && d[st]==i-t)
        {
            st++;
        }
        while(st<=dr && p[i]<=p[d[dr]]+s*(i-d[dr]))
        {
            dr--;
        }
        d[++dr]=i;
       cost_min+=(long long)c[i]*(p[d[st]]+ s*(i-d[st]));

    }
    g<<cost_min;
    return 0;
}