public int minimumTurns(String cardFront) {
		boolean[] isWhitesequence = new boolean[cardFront.length()];
		for (int i = 0; i < cardFront.length(); i++) {
			isWhitesequence[i] = cardFront.charAt(i) == 'W';
		}
		//trueならWを見てる。

		boolean current = true;
		int wcount = 0, bcount = 0;
		for (int i = 0; i < cardFront.length(); i++) {
			if (isWhitesequence[i] != current)
			{
				wcount++;
			}
			current = !current;
		}
		current = false;

		for (int i = 0; i < cardFront.length(); i++) {
			if (isWhitesequence[i] != current)
			{
				bcount++;
			}
			current = !current;
		}
		return Math.min(bcount, wcount);
	}