#include <iostream>
#include <fstream>
using namespace std;
ifstream f("branza.in");
ofstream g("branza.out");
const int N=5000001;
int c[N],p[N],dmin[N],dmax[N],stmax,stmin,drmin=-1,drmax=-1,n,t,s,i;

int main ()
{
    long long st=0;
    f>>n>>s>>t;
    t++;
    for (i=1; i<=n; i++)
        f>>c[i]>>p[i];
    for (i=1; i<=n; i++){
        if  (dmin[stmin]==i-t)
            stmin++;
        while (stmin<=drmin && c[i]<=c[dmin[drmin]]+(long long)s*(i-dmin[drmin])){
            drmin--;
        }
        dmin[++drmin]=i;
        st+=(c[dmin[stmin]]+(long long)s*(i-dmin[stmin]))*p[i];
    }
    g<<st;
    return 0;
}