#include <fstream>
#include <deque>
#include <vector>

using namespace std;

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


deque<pair<long long,long long>> bestprices;

int main()
{
    long long n,s,t;
    long long ans=0;
    in>>n>>s>>t;
    for(long long i=1; i<=n; i++){
        long long cost,quantity;
        in>>cost>>quantity;

        if(!bestprices.empty() && bestprices.front().second - i >= t)
            bestprices.pop_front();

        while(!bestprices.empty() && cost < bestprices.back().first + (i-bestprices.back().second)*s)
            bestprices.pop_back();
        bestprices.emplace_back(cost, i);

        ans += bestprices.front().first * quantity + ((long long)i-bestprices.front().second)*s*quantity;

    }
    out<<ans;
}