#include <fstream>
#include <deque>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");

deque <int> d;
int cost[100001],cant[100001],i,n,s,t,rez=0;

int main()
{
    f>>n>>s>>t;
    for (i=1; i<=n; ++i)
        f>>cost[i]>>cant[i];

    d.push_back(1);
    rez=cost[1]*cant[1];

    for (i=2; i<=n; ++i)
    {
        while (!d.empty() && cost[i]<cost[d.back()]+(i-d.back())*s)
            d.pop_back();
        d.push_back(i);

        if (i-d.front()==t) d.pop_front();

        rez+= (cost[d.front()]+(i-d.front())*s)*cant[i];
    }
    g<<rez<<'\n';
    return 0;
}