#include <fstream>
#include <deque>
#define DIM 100001
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
long long n,s,t,i,sol,c[DIM],p[DIM],v[DIM];
deque <int> dq;
int main() {
    fin>>n>>s>>t;
    for (i=1;i<=n;i++)
        fin>>c[i]>>p[i];
    dq.push_back(1);
    sol=c[1]*p[1];
    for (i=2;i<=n;i++) {
        while (!dq.empty() && c[i]<=(i-dq.back())*s+c[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (i-dq.front()==t+1)
            dq.pop_front();
        sol+=(c[dq.front()]+(i-dq.front())*s)*p[i];
    }
    fout<<sol;
    return 0;
}