#include <fstream>
#include <vector>
#include <deque>
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
int main(){
    long long n, s, t, i, x, y;
    vector<pair<long long, long long>> a;
    deque<long long> q;
    cin>>n>>s>>t;
    long long su=0;
    for(i=0;i<n;i++){
        cin>>x>>y;
        a.push_back(pair<long long,long long>(x,y));
        if(q.empty()==0 && i-q.front()-1==t){
            q.pop_front();
        }
        while(q.empty()==0 && x<=a[q.back()].first+(i-q.back())*s){
            q.pop_back();
        }
        q.push_back(i);
        su+=(a[q.front()].first+(i-q.front())*s)*y;
    }
    cout<<su;
}