#include <fstream>
std::ifstream f("branza.in");
std::ofstream g("branza.out");
long long n,s,t,v[1<<17],d[1<<17],p=1,q,c,r,i;
int main()
{
    f>>n>>s>>t;
    while(n-i++)
    {
        f>>v[i]>>c;
        while(s*(i-d[q])+v[d[q]]>v[i]&&p<=q)--q;
        d[++q]=i;
        if(i-d[p]>t)++p;
        r+=c*(s*(i-d[p])+v[d[p]]);
    }
    g<<r;
}