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