#include <fstream>
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
long long cant[100001],k,i,n,a[100001],Deque[100001],s,Back,Front,sum;
int main()
{
    fin>>n>>s>>k;
    Front=1;
    for(i=1;i<=n;i++)
        fin>>a[i]>>cant[i];
    for(i=1;i<=n;i++)
    {
        if(Deque[Front]==i-k-1)
            Front++;
        while(a[i]<=(a[Deque[Back]]+1ll*s*(i-Deque[Back]))&&Front<=Back)
            Back--;
        Deque[++Back]=i;
        sum+=1ll*(a[Deque[Front]]+(i-Deque[Front])*s)*cant[i];
    }
    fout<<sum;
    return 0;
}