#include <fstream>

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");

const int N=100001;
pair <int,int> dq[N];
int n,s,t,a,b,st=1,dr;
long long ans;

int main()
{
    fin>>n>>s>>t;
    t++;
    for(int i=1;i<=n;i++)
    {
        fin>>a>>b;
        if(i-dq[st].second==t&&st<=dr)
        {
            st++;
        }
        while(st<=dr&&dq[dr].first+s*(i-dq[dr].second)>=a)
        {
            dr--;
        }
        dq[++dr].first=a;
        dq[dr].second=i;
        ans+=b*dq[st].first+s*(i-dq[st].second)*(long long)b;
    }
    fout<<ans;
    return 0;
}