#include <fstream>

using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
int n,i,s,t,p,d[100005],c[100005],st,dr=-1;
long long sum;
inline void stanga(int i)
{
    if(st<=dr&&d[st]<i-t)
        st++;
}
inline void dreapta(int i)
{
    while(st<=dr&&c[i]<c[d[dr]]+s*(i-d[dr]))
        dr--;
    d[++dr]=i;
}
int main()
{
    cin>>n>>s>>t;
    for(i=1;i<=n;i++)
    {
        cin>>c[i]>>p;
        dreapta(i);
        stanga(i);
        sum+=(long long)(c[d[st]]+s*(i-d[st]))*p;
    }
    cout<<sum;
    return 0;
}