#include <fstream>
using namespace std;
long long n,s,t,i,p,u,sol,d[100010],c[100010],P[100010];
int main (){
    ifstream fin ("branza.in");
    ofstream fout("branza.out");
    fin>>n>>s>>t;
    for (i=1;i<=n;i++){
        fin>>c[i]>>P[i];
    }
    d[1]=1;
    p=1;
    u=1;
    sol+=c[1]*P[1];
    for (i=2;i<=n;i++){
        while (p<=u&&c[i]<=(i-d[u])*s+c[d[u]]){
            u--;
        }
        d[++u]=i;
        if (i-d[p]==t+1){
            p++;
        }
        sol+=(c[d[p]]+s*(i-d[p]))*P[i];
    }
    fout<<sol;
    return 0;
}