#include <fstream>

using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
int v[100001],d[100001];
int main()
{
    int n,s,t,st,dr,i,p;
    long long sum=0;
    cin>>n>>s>>t;
    st=0;
    dr=-1;
    for(i=0;i<n;i++)
    {
        cin>>v[i]>>p;
        if(st<=dr&&d[st]==i-t)
           st++;
        while(st<=dr&&v[i]<=v[d[dr]]+s*(i-d[dr]))
              dr--;
        d[++dr]=i;
        sum+=p*(v[d[st]]+s*(i-d[st]));
    }
    cout<<sum;
    return 0;
}