#if __INCLUDE_LEVEL__ == 0

#include __BASE_FILE__

namespace {

void solve() {
  constexpr Float PHI = std::numbers::phi_v<Float>;

  Str s;
  scan(s);
  Int n = len(s);
  Map<Tuple<Int, Int>, Tuple<Int, Float, Float>> f;
  f[{}] = {};
  for (ans : rep(inf())) {
    Map<Tuple<Int, Int>, Tuple<Int, Float, Float>> nf;
    for ([key, val_] : f) {
      auto [a, b] = key;
      auto [val, min, max] = val_;
      if (val == n) {
        print(ans);
        return;
      }
      {
        Int na = a + 1;
        Int nb = b;
        Float nmin = std::min(min, na - nb * PHI);
        Float nmax = std::max(max, na - nb * PHI);
        if (nmax - nmin < 1 + PHI) {
          Int nval = val + (s[val] == 'a');
          chmax(nf[{na, nb}], {nval, nmin, nmax});
        }
      }
      {
        Int na = a;
        Int nb = b + 1;
        Float nmin = std::min(min, na - nb * PHI);
        Float nmax = std::max(max, na - nb * PHI);
        if (nmax - nmin < 1 + PHI) {
          Int nval = val + (s[val] == 'b');
          chmax(nf[{na, nb}], {nval, nmin, nmax});
        }
      }
    }
    f = std::move(nf);
  }
}

}  // namespace

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cout << std::setprecision(std::numeric_limits<Float>::max_digits10);

  solve();
}

#else  // __INCLUDE_LEVEL__

#include <bits/stdc++.h>

using Int = int64_t;
using Float = float;
using Str = std::string;

template <class T1, class T2>
using Pair = std::pair<T1, T2>;

template <class... Ts>
using Tuple = std::tuple<Ts...>;

template <class T, size_t N>
using Arr = std::array<T, N>;

template <class T>
using Vec = std::vector<T>;

template <class T>
using Set = std::set<T>;

template <class T>
using Multiset = std::multiset<T>;

template <class K, class T>
using Map = std::map<K, T>;

template <class T>
using MinHeap = std::priority_queue<T, Vec<T>, std::greater<T>>;

template <class T>
using MaxHeap = std::priority_queue<T>;

namespace ranges = std::ranges;
namespace views = std::views;

inline constexpr auto len = ranges::ssize;
inline constexpr auto rev = views::reverse;

constexpr auto rep(Int l, Int r) { return views::iota(std::min(l, r), r); }
constexpr auto rep(Int n) { return rep(0, n); }
constexpr auto rep1(Int l, Int r) { return rep(l, r + 1); }
constexpr auto rep1(Int n) { return rep(1, n + 1); }

template <class T, class U = T>
bool chmin(T& x, U&& y) {
  return y < x && (x = std::forward<U>(y), true);
}

template <class T, class U = T>
bool chmax(T& x, U&& y) {
  return x < y && (x = std::forward<U>(y), true);
}

template <std::signed_integral T = Int>
T inf() {
  T ret;
  std::memset(&ret, 0x3f, sizeof(ret));
  return ret;
}

template <std::floating_point T>
T inf() {
  return std::numeric_limits<T>::infinity();
}

template <class T>
concept Range = ranges::range<T> && !std::convertible_to<T, std::string_view>;

template <class T>
concept TupleLike = std::__is_tuple_like<T>::value && !Range<T>;

namespace std {

istream& operator>>(istream& is, Range auto&& r) {
  for (auto&& e : r) {
    is >> e;
  }
  return is;
}

istream& operator>>(istream& is, TupleLike auto&& t) {
  return apply([&](auto&... xs) -> istream& { return (is >> ... >> xs); }, t);
}

ostream& operator<<(ostream& os, Range auto&& r) {
  for (string_view sep = ""; auto&& e : r) {
    os << exchange(sep, " ") << e;
  }
  return os;
}

ostream& operator<<(ostream& os, TupleLike auto&& t) {
  const auto f = [&](auto&... xs) -> ostream& {
    [[maybe_unused]] string_view sep = "";
    ((os << exchange(sep, " ") << xs), ...);
    return os;
  };
  return apply(f, t);
}

}  // namespace std

#define DEF_INC_OR_DEC(op) \
  auto& operator op(Range auto&& r) { \
    for (auto&& e : r) { \
      op e; \
    } \
    return r; \
  } \
  auto& operator op(TupleLike auto&& t) { \
    std::apply([](auto&... xs) { (op xs, ...); }, t); \
    return t; \
  }

DEF_INC_OR_DEC(++)
DEF_INC_OR_DEC(--)

#undef DEF_INC_OR_DEC

void scan(auto&&... xs) { std::cin >> std::tie(xs...); }
void print(auto&&... xs) { std::cout << std::tie(xs...) << '\n'; }

template <class F>
class fix {
 public:
  explicit fix(F f) : f_(std::move(f)) {}

  decltype(auto) operator()(auto&&... xs) const {
    return f_(std::ref(*this), std::forward<decltype(xs)>(xs)...);
  }

 private:
  F f_;
};

#define for(...) for ([[maybe_unused]] auto&& __VA_ARGS__)

#endif  // __INCLUDE_LEVEL__