#include<fstream>
#include<deque>
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");

int n,s,t,x,y;
int v[100005],c[100005];
deque<int> d;
long long ans;

int main(){

    cin>>n>>s>>t;
    for(int i=1;i<=n;i++){

        cin>>v[i]>>c[i];

        while(!d.empty() && v[d.back()]+1LL*(i-d.back())*s>=v[i]) d.pop_back();
        d.push_back(i);
        if(d.front()==i-t-1) d.pop_front();

        ans+=(v[d.front()]+1LL*(i-d.front())*s)*c[i];

    }

    cout<<ans;

}