#include <queue>
#include <fstream>
#include <vector>
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");

int main(){

    int n, s, t, i, x, y;
    vector<pair<int, int>> a;
    vector<priority_queue<int>> b;
    priority_queue<int> aux;
    cin>>n>>s>>t;
    b.assign(n, aux);
    for(i=0;i<n;i++){
        cin>>x>>y;
        a.push_back(pair<int,int>(x,y));
        b[i].push(-x*y);
    }
    for(i=0;i<n-1;i++){
        int j=1;
        while(j<=t && i+j<n){
            b[i+j].push(-(a[i].first*a[i+j].second+a[i+j].second*j*s));
            j++;
        }
    }
    int v=0;
    for(auto i: b){
        v+=i.top();
    }
    cout<<-v;

}