#include <fstream>
#define dim 100001
using namespace std;
ifstream fin ("branza.in");
ofstream fout ("branza.out");
int n, s, t, i, c[dim], p[dim], cont[dim], sol, j, val;
int main()
{
    fin>>n>>s>>t;
    for (i=1; i<=n; i++)
        fin>>c[i]>>p[i];
    for (i=1; i<=n; i++)
    {
        if (cont[i]==0)
            cont[i]=c[i]*p[i];
        else
            cont[i]=min(cont[i], c[i]*p[i]);
        for (j=1; j<=t, i+j<=n; j++)
        {
            val=j*s+c[i];
            if (cont[i+j]!=0)
                cont[i+j]=min (cont[i+j], val*p[i+j]);
            else
                cont[i+j]=val*p[i+j];
        }
    }
    for (i=1; i<=n; i++)
        sol+=cont[i];
    fout<<sol;
}