#include <bits/stdc++.h>
using namespace std;

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

deque<int> d;
int i,n,s,t,c[100001],p[100001];
long long sum=0;
int main()
{
    fin>>n>>s>>t;
    for(i=0; i<n; i++){
        fin>>c[i]>>p[i];

        if(!d.empty() && d.front() == i-t)
            d.pop_front();

        while(!d.empty() && c[i]<=c[d.back()] + s*(i-d.back()))
            d.pop_back();

        d.push_back(i);

        sum+= p[i]*(c[d.front()]+ s*(i-d.front()));
    }
    cout<<sum;
    return 0;
}