#include <iostream>
#include <fstream>
#include <deque>

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

const int NMAX = 100'005;
int n,s,t,v[NMAX],c[NMAX],p[NMAX],sol;
std::deque<int>d;

//c[] - costul de productie 1 kg
//p[] - cantitatea pentru o anumita saptamana

int main(){
    
    f >> n >> s >> t;
    
    for(int i = 1;i <= n;++i)
        f >> c[i] >> p[i];
    
    sol += c[1] * p[1];
    d.push_back(1);
    
    for(int i = 2;i <= n;++i){
        
        while(!d.empty() && c[i] <= (i - d.back()) * s + c[d.back()])
            d.pop_back();
        
        d.push_back(i);
        
        if(i - d.front() > t)
            d.pop_front();
        
        sol = sol + ( (i - d.front()) * s + c[d.front()] * p[i]);
    }
    
    g << sol;
    
    return 0;
}