#include <fstream>
using namespace std;
ifstream f ("branza.in");
ofstream g ("branza.out");
long long n,s,t,v[100003],d[100003],p=1,q,c,sol;
int main()
{
    f>>n>>s>>t;
    for(int i=1;i<=n;++i)
    {
        f>>v[i]>>c;
        while(s*(i-d[q])+v[d[q]]>=v[i]&&p<=q) --q;
        ++q;
        d[q]=i;
        if(i-d[p]>t) ++p;
        sol+=c*(s*(i-d[p])+v[d[p]]);
    }
    g<<sol;
    return 0;
}