import java.util.*;

public class Run {
    public static void main (String arg[]) {
        Scanner scan = new Scanner(System.in);
        int ans = 0;
        int n = 1000;

        double N, K;
        boolean turn = true;

        for (int i = 0; i < n; i++) {
            N = scan.nextDouble();
            K = scan.nextDouble();

            if (turn) {
                if (N < K - 1) {
                    ans++;
                    turn = false;
                }
                else if ((N - 1)%(K + 1)==0) {
                    ans++;
                    turn = false;
                }
            } else {
                if (N < K - 1) turn = true;
                else if ((N - 1)%(K + 1)!=0) {
                    ans++;
                } else turn = true;
            }
        }

       System.out.println(ans);
    }
}