///TEST

#include <bits/stdc++.h>

using namespace std;

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

struct str{
    int c,p;
}v[100001];

long long nrb,cost,cant;

int main()
{
    long long n,s,t,c,p,i,j;

    f>>n>>s>>t;

    for(i=1;i<=n;++i)
        f>>v[i].c>>v[i].p;

    for(i=1;i<=n;++i){
        if(nrb>=v[i].p){
            nrb-=v[i].p;
            continue;
        } else {
            cost+=v[i].c*v[i].p;

            for(j=i+1;j<=n && j<=i+t;++j){
                if(v[j].c*v[j].p>v[i].c*v[j].p+v[j].p*((j-i)*s)){
                    cost+=v[i].c*v[j].p+v[j].p*((j-i)*s);
                    nrb+=v[j].p;
                } else break;
            }
        }
    }

    g<<cost;

    return 0;
}