#include<fstream>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
long long v[100010],d[100010],n,taxa,days;
long long sum;
int main()
{
    f>>n>>taxa>>days;
    long long head=1,tail=0,i,p;
    for(i=1;i<=n;++i)
    {
        f>>v[i]>>p;
        while(head<=tail&&v[i]<v[d[tail]]+((i-d[tail])*taxa))
          tail--;
        d[++tail]=i;
        while(head<=tail&&i-d[head]>days)
          head++;
        sum+=(long long)(v[d[head]]+(i-d[head])*taxa)*p;
    }
    g<<sum;
    return 0;
}