#include <fstream>
#include <deque>

using namespace std;

ifstream cin("branza.in");
ofstream cout("branza.out");

const int N = 1e5;
int c[N];

int main()
{
    int n,storage_p,max_t;
    cin>>n>>storage_p>>max_t;
    deque <int> minCost;
    int totalP=0;
    for(int i=0;i<n;++i)
    {
        int pret;
        cin>>c[i]>>pret;
        if(!minCost.empty() && i-max_t-1==minCost.front())
            minCost.pop_front();
        while(!minCost.empty() && c[i]<(c[minCost.back()]+storage_p*(i-minCost.back())))
            minCost.pop_back();
        minCost.push_back(i);
        totalP += pret * ( c[minCost.front()] + storage_p * (i-minCost.front()) );
    }
    cout<<totalP;
    return 0;
}