//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <utility>
#include <vector>

namespace n91 {

  using i8 = std::int_fast8_t;
  using i32 = std::int_fast32_t;
  using i64 = std::int_fast64_t;
  using u8 = std::uint_fast8_t;
  using u32 = std::uint_fast32_t;
  using u64 = std::uint_fast64_t;
  using isize = std::ptrdiff_t;
  using usize = std::size_t;

  struct rep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { ++i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  struct revrep {
    struct itr {
      usize i;
      constexpr itr(const usize i) noexcept : i(i) {}
      void operator++() noexcept { --i; }
      constexpr usize operator*() const noexcept { return i; }
      constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
    };
    const itr f, l;
    constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
    constexpr auto begin() const noexcept { return f; }
    constexpr auto end() const noexcept { return l; }
  };
  template <class T> auto md_vec(const usize n, const T& value) {
    return std::vector<T>(n, value);
  }
  template <class... Args> auto md_vec(const usize n, Args... args) {
    return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
  }
  template <class T> constexpr T difference(const T& a, const T& b) noexcept {
    return a < b ? b - a : a - b;
  }
  template <class T> void chmin(T& a, const T& b) noexcept {
    if (b < a)
      a = b;
  }
  template <class T> void chmax(T& a, const T& b) noexcept {
    if (a < b)
      a = b;
  }
  template <class F> class rec_lambda {
    F f;

  public:
    rec_lambda(F&& f) : f(std::move(f)) {}
    template <class... Args> auto operator()(Args&&... args) const {
      return f(*this, std::forward<Args>(args)...);
    }
  };
  template <class F> auto make_rec(F&& f) { return rec_lambda<F>(std::move(f)); }
  template <class T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }
  constexpr char eoln = '\n';
  template <class T> T ceildiv(const T& l, const T& r) {
    return l / r + (l % r != 0 ? 1 : 0);
  }

} // namespace n91

namespace n91 {

  usize solve(const std::string& s, isize cc) {
    // cc = 0 or 1;
    isize c = cc;

    const usize n = s.size();

    std::vector<usize> down;
    for (const usize i : rep(0, n)) {
      const auto e = s[i];
      switch (e) {
      case '0': {
        c += 1;
      } break;
      case '1': {
        c -= 1;
      } break;
      case '?': {
        c -= 1;
        down.push_back(i);
      } break;
      }
      if (c == -1) {
        down.pop_back();
        c += 2;
      }
    }

    std::vector<bool> is_down(n, false);
    for (const auto e : down) {
      is_down[e] = true;
    }

    isize pos = cc;
    isize res = cc;

    for (const usize i : rep(0, n)) {
      const auto e = s[i];
      switch (e) {
      case '0': {
        pos += 1;
      } break;
      case '1': {
        pos -= 1;
      } break;
      case '?': {
        if (is_down[i]) {
          pos -= 1;
        }
        else {
          pos += 1;
        }
      } break;
      }
      chmax(res, pos);
    }

    return res;
  }

  void main_() {
    //*
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    //*/

    const std::string s = scan<std::string>();
    const usize n = s.size();

    isize pos = 0;
    isize min = 0;
    usize mindex = 0;

    for (const usize i : rep(0, n)) {
      switch (s[i]) {
      case '0': {
        pos += 1;
      } break;
      case '1': {
        pos -= 1;
      } break;
      }
      if (min > pos) {
        min = pos;
        mindex = i + 1;
      }
    }

    usize ans = n;

    {
      std::string l = s.substr(0, mindex);
      std::string r = s.substr(mindex, n - mindex);
      std::reverse(l.begin(), l.end());
      for (auto& e : l) {
        if (e == '0') {
          e = '1';
        }
        else if (e == '1') {
          e = '0';
        }
      }
      chmin(ans, std::max(solve(l, 0), solve(r, 0)));
      chmin(ans, std::max(solve(l, 1), solve(r, 1)));
    }

    std::cout << ans << eoln;
  }

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 13164