public class CountA {
	public static int count_a(String str) {

		// Verwenden Sie dafür nur eine for-Schleife und eine if-Abfrage
		// Sie dürfen die Methoden length() und charAt(int i) der Klasse String verwenden 	
		
		int i = 0;
		for (int j = 0; j < str.length(); j++) {
			if ( str.charAt(j) == 'a' ) {
				i++;
			}
			else {
				
			
			}
		}
		return i;
	}

	public static void main(String[] args) {
		assert (count_a("") == 0);
		assert (count_a("a") == 1);
		assert (count_a("aa") == 2);
		assert (count_a("abb ") == 1);
		assert (count_a(" abba ") == 2);
		assert (count_a("bb") == 0);
		System.out.println(" Everything good !");
	}
}