#include <fstream>
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
const int nm=100005;
long long n,s,t,d[nm],st=1,dr=0,sum=0;
struct fint
{
    long long c,p;
};
fint v[nm];
int main()
{
    cin>>n>>s>>t;
    for(int i=1;i<=n;i++)
        cin>>v[i].c>>v[i].p;
    t++;
    for(int i=1;i<=n;i++)
    {
        if(st<=dr and d[st]==i-t)
            st++;
        while(st<=dr and v[i].c<=v[d[dr]].c+s*(i-d[dr]))
            dr--;
        d[++dr]=i;
        sum+=(long long)v[i].p*(v[d[st]].c+s*(i-d[st]));
    }
    cout<<sum;
    return 0;
}