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

using namespace std;

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

#define int unsigned long

struct Info {
    int price;
    int to_beBought;
};

struct InfoDeque {
    int val;
    int idx;
    InfoDeque() {}
    InfoDeque(int val,int idx) {
        this->val = val;
        this->idx = idx;
    }
    bool operator<(InfoDeque a2) const {
        return val<a2.val;
    }
};

int n,price_toKeepPerKg,maxPeriodToKeep;
vector<Info> v;

void read() {
    cin>>n>>price_toKeepPerKg>>maxPeriodToKeep;
    v.resize(n+1);
    for(int i=1;i<=n;i++) {
        cin>>v[i].price>>v[i].to_beBought;
    }
}

void solve() {
    deque<InfoDeque> dq;
    vector<int> dp(n+1);
    for(int i=1;i<=n;i++) {
        while(!dq.empty() && dq.back().val >= v[i].price + (n-i+1) * price_toKeepPerKg) {
            dq.pop_back();
        }
        while(dq.size() > maxPeriodToKeep) {
            dq.pop_front();
        }
        dq.push_back((*new InfoDeque(v[i].price + (n-i+1) * price_toKeepPerKg, i)));
        dp[i] = min(v[i].price, v[dq.front().idx].price + ((i-dq.front().idx) * price_toKeepPerKg));
    }
    int rs=0;
    for(int i=1;i<=n;i++) {
        rs+=dp[i] * v[i].to_beBought;
    }
    cout<<rs;
}

int32_t main() {

    read();
    solve();
    return 0;
}