#include <fstream>
#include <deque>
#define sz 100000
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");

long long n,s,t;

long long sol;

long long c[sz + 5];
long long p[sz + 5];

deque <long long> q;

int main()
{
    fin>>n>>s>>t;
    for(int i=1;i<=n;i++){
        fin>>c[i]>>p[i];
        while(!q.empty() && i-q.front()+1>t)
            q.pop_front();
        while(!q.empty() && c[i] <= c[q.back()] + (i-q.back())*s)
            q.pop_back();
        q.push_back(i);
        sol += (c[q.front()] + (i-q.front())*s)*p[i];
    }
    fout<<sol;


}