#include <fstream>
using namespace std;
ifstream fin ("branza.in");
ofstream fout ("branza.out");
long long n,s,t,p,q,sum,i,c,nr,d[100001],v[100001];
int main ()
{
    fin>>n>>s>>t;
    p=1;
    q=0;
    for (i=1; i<=n; i++)
    {
        fin>>c>>nr;
        v[i]=c;
        while (p<=q&&c<=v[d[q]]+(i-d[q])*s)
            q--;
        d[++q]=i;
        sum=sum+(v[d[p]]+(i-d[p])*s)*nr;
        if (i-d[p]==t)
            p++;
    }
    fout<<sum;
    return 0;
}