#include <bits/stdc++.h>

using namespace std;

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

const int NMAX =100001;
int v[NMAX],dq[NMAX],n,s,t,p,ans;

int main()
{
    in>>n>>s>>t;
    int st=0;
    int dr=-1;
    for(int i=0; i<=n; ++i)
    {
        in>>v[i]>>p;
        if (i>=t && dq[st]==i-t)
        {
            st++;
        }
        while (st<=dr && v[i]<=v[dq[dr]]+s*(i-dq[dr]))
        {
            dr--;
        }
        dq[++dr]=i;
        ans+=p*(v[dq[st]]+s*(i-dq[st]));
    }
    out<<ans;
    return 0;
}