#include <fstream>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");

int bani;

int main()
{
    int n,s,t,v[100000][2],c,i;
    f>>n>>s>>t;
    for(i=1;i<=n;i++)
        f>>v[i][0]>>v[i][1];
    for(i=1;i<=n;i++)
    {
        bani+=v[i][0]*v[i][1];
        c=1;
        while(v[i+c][0]>v[i][0]+s*c && c<=t && i+c<=n)
        {
            bani+=(v[i][0]+s*c)*v[i+c][1];
            c++;
        }
        i+=c-1;
    }
    g<<bani;
}