#include <fstream>

using namespace std;

ifstream in("branza.in");
ofstream out("branza.out");

int v[100005];
int dq[100005];

int main()
{
    lon long cost=0;
    int n,s,k;
    in>>n>>s>>k;
    int st=0,dr=-1;
    t++;
    for(int i=0; i<=n; i++)
    {
        int p;
        in>>v[i];
        in>>p;
        if(i>=k && dq[st]==i-k)
        {
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]]+s*(i-dq[dr]))
        {
            dr--;
        }
        dq[++dr]=i;
        cost+=(long long)p*(v[dq[st]]+s*(i-dq[st]));
    }
    out<<cost;
    return 0;
}