#include <fstream>
#include <deque>
#include <vector>

using namespace std;

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

vector<pair<int,int>> v;

int main()
{
    int n,s,t;
    long long ans=0;
    in>>n>>s>>t;
    for(int i=0; i<n; i++){
        int c,p;
        in>>c>>p;
        v.emplace_back(c,p);
        int bestprice = c;
        for(int index=i-1; index>=max(0, i-t); index--){
            bestprice = min(bestprice, v[index].first + (i-index)*s);
        }
        ans+=bestprice*p;
    }
    out<<ans;
}