public class Count3Quit {


	public static void main (String[] args){

		boolean [] arr = new boolean[500];

		int len = arr.length;
		for (int i = 0; i < len ; i++) {

			arr [i] = true;
		}

		int leftCount = len;
		int countNum = 0;
		int index = 0;

		while (leftCount > 0 ){

			if (arr[index]==true){

				countNum++;
				if (countNum==3){

					countNum = 0;
					arr[index] = false;
					leftCount --;
				}
			}
			index++;

			if (index == len ) {

				index = 0;
			}
		}

		for (int i = 0; i < len ; i++) {

			if (arr[i] == true ){

				System.out.println(i);
			}
		}
	}
}
 

輸出的是下標值，所以是第i+1個。