#include <fstream>
#include <vector>
#include <deque>
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
int N,S,T,x;
int main()
{
	fin>>N>>S>>T;
	vector<int>v(N);
	deque<int>dq(N);
	long long total=0;
	for(int i=0; i<N; i++)
	{
		long long cost=0;
		fin>>v[i]>>x;
		while(!dq.empty() && v[dq.back()]>=v[i])
			dq.pop_back();
		dq.push_back(i);
		if(dq.front()==i-T-1)
			dq.pop_front();
		cost=1LL*v[dq.front()]*x+S*(i-dq.front());
		if(1LL*v[i]*x<=cost)
			total+=cost;
		else
			total+=1LL*v[i]*x;
	}
	fout<<total;
	return 0;
}