#include <bits/stdc++.h>

using namespace std;

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

deque <long long> q;
long long n,S,t,i,min_val,cant,suma,cost[100100];

int main()
{
    f>>n>>S>>t;

    for(i=1;i<=n;i++)
    {
        f>>cost[i]>>cant;

        while(!q.empty() && cost[i]<=(cost[q.back()]+S*(i-q.back())))q.pop_back();
        q.push_back(i);
        while(i-q.front()>t)q.pop_front();

        min_val=cost[q.front()]+S*(i-q.front());
        suma+=min_val*cant;
    }

    g<<suma;
    return 0;
}