#include <bits/stdc++.h>

using namespace std;

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


deque<int> deq;

long long v[100005],n,p,s,t, cost;

int main()
{
    fin>>n>>s>>t;
    t=t+1;
    for(long long i=1; i<=n; i++)
    {
        fin>>v[i]>>p;
        if(deq.size()!=0 and deq.front()==i-t)
        {
            deq.pop_front();
        }
        while(deq.size()!=0 and v[deq.back()]+s*(i-deq.back())>=v[i])
        {
            deq.pop_back();
        }
        deq.push_back(i);
        cost+=p*(v[deq.front()]+s*(i-deq.front()));
    }
    fout<<cost<<endl;
    return 0;
}