#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();
  ll l = 0, r = n;
  while (r - l > 1) {
    ll m = (l + r) / 2;
    bool flg = false;
    for (ll t = (0); (t) < (2); ++(t)) {
      ll mi = t, ma = m;
      if (mi & 1 != ma & 1) --ma;
      bool ok = true;
      for (ll i = (0); (i) < (n); ++(i)) {
        if (s[i] == '0') {
          --ma;
          --mi;
        } else if (s[i] == '1') {
          ++ma;
          ++mi;
        } else {
          ++ma;
          --mi;
        }
        if (ma > m) ma -= 2;
        if (mi < 0) mi += 2;
        if (ma < mi) ok = false;
      }
      flg |= ok;
    }
    if (flg)
      r = m;
    else
      l = m;
  }
  co(r);
  return 0;
}
