#include <fstream>

using namespace std;

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

int v[100001],p[100001],s,n,t,dq[100001],k;
long long nr;

int main()
{
    fin>>n>>s>>t;
    int st=0,dr=-1;
    for(int i=0;i<n;i++){
        fin>>v[i]>>p[i];
        while(st<=dr && dq[st]==i-t)
            st++;
        while(st<=dr && v[i]<=v[dq[dr]]+(i-dq[dr])*s)
            dr--;
        dq[++dr]=i;
        nr+=(v[dq[st]]+s*(i-dq[st]))*p[i];
    }
    fout<<nr;
    return 0;
}