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

int n, s, t, v[100002], d[100002], p=1, q, c, rasp;  

int main(){
	int player_unu=0;

	in>>n>>s>>t;
	for(int i = 1; i<=n; i++)
	{
		in>>v[i]>>c;

		while(s * (i - d[q]) + v[d[q]]>=v[i] && p<=q)
			q--;

		q++;
		d[q] = i;

		if(i - d[p]>=s)
			p++;

		rasp += c * (s * (i - d[p]) + v[d[p]]);
	}

	out<<rasp<<'\n';
	return player_unu;
}