#include <fstream>
#include <queue>

using namespace std;

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

const int nmax=100000;

int c[nmax+1], p[nmax+1];

deque <int> dq;

int main(){
    int n,s,t;
    fin>>n>>s>>t;
    for(int i=1;i<=n;i++){
        fin>>c[i]>>p[i];
    }
    int sol=0;
    for(int i=1;i<=n;i++){
        while(dq.empty()==0&&c[dq.back()]+(i-dq.back())*s>c[i]){
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front()<=i-t){
            dq.pop_front();
        }
        sol+=(c[dq.front()]+(i-dq.front())*s)*p[i];
    }
    fout<<sol<<"\n";
    return 0;
}