import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner inputScanner = new Scanner(System.in);
int n = inputScanner.nextInt();
int k = inputScanner.nextInt();
int[] list1 = new int[k];
int[] list2 = new int[k];
for (int i = 0; i < k; i++) {
list1[i] = inputScanner.nextInt();
list2[i] = inputScanner.nextInt();
}
int sum = 0;
int temp = 0;
for (int i = 0; i < k; i++) {
if (list2[i] == 0) {
temp++;
} else {
for (int j = 0; j < i; j++) {
if (list2[i] == list1[j]) {
sum++;
break;
}
}
}
}
System.out.println(k - sum - temp);
inputScanner.close();
}
}