#include <fstream>
#include <deque>

using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");

const int N=100005;
int v[N];

deque <int>  d;

long long sum;
int n,s,t,k;
void citire()
{
    fin>>n>>s>>t;
    ++t;
    for(int i=1; i<=n; ++i)
    {
        fin>>v[i]>>k;
        if(!d.empty() and d.front()==i-t)
            d.pop_front();
        while(!d.empty()  and v[d.back()]+(i-d.back())*s>=v[i])
            d.pop_back();
        d.push_back(i);
        sum+=(long long)k*(v[d.front()]+(i-d.front())*s);

    }


}
int main()
{
    citire();
    fout<<sum<<'\n';
}