def isPerfectSquare(num):
    if num < 1:
        return False
    left, right = 1, num
    while left <= right:
        mid = left + (right - left) // 2
        square = mid * mid
        if square == num:
            return True
        elif square < num:
            left = mid + 1
        else:
            right = mid - 1
    return False