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

int main(){

    int n, s, t, i, x, f, y;
    vector<pair<int, int>> a;
    cin>>n>>s>>t;
    int v=0;
    int su=0;
    for(i=0;i<n;i++){
        cin>>x>>y;
        a.push_back(pair<int,int>(x,y));
        int j=-1;
        v=a[i].first*a[i].second;
        while(i+j>0 && -j<t){
            f=a[i+j].first*a[i].second+a[i].second*(-j)*s;
            if(v>f){
                v=f;
            }
            j--;
        }
        su+=v;
    }
    cout<<su;
}