以下程序段运行后，输入：ABCdef，输出应为？

char ch;
while ((ch = getchar()) != '\n') {
    if (ch >= 'A' && ch <= 'Z')
        ch = ch + 32;
    else if (ch >= 'a' && ch <= 'z')
        ch = ch - 32;
    cout << ch;
}