#include <fstream>
#include <deque>
#include <algorithm>

using namespace std;

const int NMAX = 100005;

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

int price[NMAX], order[NMAX];

int main()
{
    int n, s, t;
    cin>>n>>s>>t;
    long long rez = 0;
    long long best = 0;
    int poz = 1;
    for(int i = 1; i <= n; ++i) {
        cin>>price[i]>>order[i];
        if(i == 1)
        {
            best = price[i];
            poz = i;
            rez = price[i] * order[i];
            continue;
        }
        if(best + s * (i - poz) > price[i]) {
            best = price[i];
            poz = i;
        }
        rez += (best + s * (i - poz)) * order[i];
    }
    cout<<rez<<"\n";
    return 0;
}