#include <fstream>
#include <deque>
#include <vector>

#define ll long long

using namespace std;

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


deque<pair<ll, ll>> bestprices;

int main()
{
    ll n,s,t;
    ll ans=0;
    in>>n>>s>>t;
    for(int i=1; i<=n; i++){
        ll cost,quantity;
        in>>cost>>quantity;

        while(!bestprices.empty() && cost < bestprices.back().first + (i-bestprices.back().second)*s)
            bestprices.pop_back();
        bestprices.emplace_back(cost, i);

        while(!bestprices.empty() && i- bestprices.front().second > t)
            bestprices.pop_front();

        ans += bestprices.front().first * quantity + (i-bestprices.front().second)*s*quantity;

    }
    out<<ans;
}