#define SIZE 100005
#include <fstream>
using namespace std;

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

struct saptamana{ int c, p;
                }v[SIZE];

int n, s, t, nr, dq[SIZE];

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