#include <iostream>
#include <fstream>
using namespace std;
int c[1000000], v[1000000], d[1000000];

int main()
{
    ifstream in("branza.in");
    ofstream out("branza.out");
    int st=0, dr=-1,i,n,s,t;
    long long suma=0;
    in>>n>>s>>t;
    for (i=0; i<n; i++)
       {
            in>>c[i]>>v[i];
            if(st<=dr && d[st]==i-t)
            {
                st++;
            }
            while(st<=dr && c[i]<=c[d[dr]]+ s*(i - d[dr]))
            {
                dr--;
            }
            d[++dr]=i;
            suma+=v[i]*(c[d[st]] + s*(i-d[st]));
       }
       out<<suma;

        return 0;
}