#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream si("branza.in");
ofstream so("branza.out");
deque<int> c;
deque<int> p;
int main()
{
    int n,s,k;
    si>>n>>s>>k;
    int i,a,b;
    long long cost=0;
    for(i=1;i<=n;++i)
    {
        si>>a>>b;
        while(!c.empty()&&c.back()+s*(i-p.back())>a)
        {
            c.pop_back();
            p.pop_back();
        }
        c.push_back(a);
        p.push_back(i);
        if(p.front()<i-k)
        {
            p.pop_front();
            c.pop_front();
        }
        cost+=1LL*b*(c.front()+s*(i-p.front()));
    }
    so<<cost<<'\n';
    return 0;
}