#include <fstream>
#include <deque>
#define cost first
#define timp second
using namespace std;
ifstream cin("branza.in");
ofstream cout("branza.out");
int n,s,t,p,c;
long long sol;
deque<pair<int,int>>q;
int main()
{
    cin>>n>>s>>t;
    for(int i=1;i<=n;i++){
        cin>>p>>c;
        while(!q.empty()&&i-q.front().timp>t)
            q.pop_front();
        while(!q.empty()&&q.back().cost+s*(i-q.back().timp)>=p)
            q.pop_back();
        q.push_back({p,i});
        sol+=1LL*(q.front().cost+s*(i-q.front().timp))*c;
    }
    cout<<sol;
    return 0;
}