#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
using Graph = vector<VecP>;
template <typename T>
using Vec1 = vector<T>;
template <typename T>
using Vec2 = vector<Vec1<T> >;
template <typename T>
bool chmax(T &a, const T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
bool chmin(T &a, const T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
ll pow2(const T n) {
  return (1LL << n);
}
template <typename T>
void cosp(const T n) {
  cout << n << ' ';
}
void co(void) { cout << '\n'; }
template <typename T>
void co(const T n) {
  cout << n << '\n';
}
template <typename T1, typename T2>
void co(pair<T1, T2> p) {
  cout << p.first << ' ' << p.second << '\n';
}
template <typename T>
void co(const Vec1<T> &v) {
  for (T i : v) cosp(i);
  co();
}
template <typename T>
void co(initializer_list<T> v) {
  for (T i : v) cosp(i);
  co();
}
template <typename T>
void ce(const T n) {
  cerr << n << endl;
}
void sonic() {
  ios::sync_with_stdio(false);
  cin.tie(0);
}
void setp(const ll n) { cout << fixed << setprecision(n); }
constexpr int INF = 1e9 + 1;
constexpr ll LINF = 1e18 + 1;
constexpr ll MOD = 1e9 + 7;
constexpr ld EPS = 1e-11;
const ld PI = acos(-1);
int main(void) {
  string s;
  cin >> s;
  ll n = s.size();
  Vec cs(n + 1);
  for (ll i = (n)-1; (i) >= (0); --(i)) {
    if (s[i] == '1')
      cs[i] = cs[i + 1] + 1;
    else
      cs[i] = max(0LL, cs[i + 1] - 1);
  }
  ll l = -1, r = n;
  ll ans = n;
  while (r - l > 1) {
    ll m = (l + r) / 2;
    ll p = 0, min = 0;
    bool flg = true;
    for (ll i = (0); (i) < (n); ++(i)) {
      if (s[i] == '1')
        ++p;
      else if (s[i] == '0')
        --p;
      else {
        if (p + 1 + cs[i + 1] <= m)
          ++p;
        else
          --p;
      }
      if (p > m) {
        flg = false;
        break;
      }
      chmin(min, p);
    }
    if (flg) {
      chmin(ans, m - min);
      r = m;
    } else
      l = m;
  }
  co(ans);
  return 0;
}
