#include <fstream>
#include <deque>
#define NMAX 100000
using namespace std;
int n, t, s, p, c[NMAX+2];
deque <int> dqmin;
long long sol;
int main()
{
    ifstream fin ("branza.in");
    ofstream fout ("branza.out");

    fin>>n>>s>>t;
    for(int i=1; i<=n; i++)
    {
        fin>>c[i]>>p;
        while(!dqmin.empty() && c[i]-i*s<=c[dqmin.back()]-dqmin.back()*s)
            dqmin.pop_back();
        dqmin.push_back(i);

        sol+=(long long)(c[dqmin.front()]+(i-dqmin.front())*s)*p;

        if(i-dqmin.front()==t)///t sapt in urma, i-dqmin.front()+1=t+1, caci lungimea unui interval este de fapt t+1
            dqmin.pop_front();
    }
    fout<<sol;
    return 0;
}