#include<fstream>
#include<deque>
using namespace std;
ifstream fin ("branza.in");
ofstream fout("branza.out");
int c[100001], q[100001], s, t;
long long n, i;
deque<int>dq;
int main(){
    fin >> n >> s >> t;
    long long sum=0;
    for(i=1;i<=n;i++){
        fin >> c[i] >> q[i];
        while(!dq.empty() && c[i]<=c[dq.back()]+(i-dq.back())*s)
            dq.pop_back();
        dq.push_back(i);
        if(i-dq.front()==t+1)
            dq.pop_front();
        sum+=c[dq.front()]*q[i]+(i-dq.front())*s*q[i];
    }
    fout << sum;
}