#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define dump(x)                                                                \
  if (dbg) {                                                                   \
    cerr << #x << " = " << (x) << endl;                                        \
  }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  } else
    return 0;
}
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  } else
    return 0;
}
void Yes(bool flag = true) {
  if (flag)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
void No(bool flag = true) { Yes(!flag); }
void YES(bool flag = true) {
  if (flag)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
void NO(bool flag = true) { YES(!flag); }
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}
bool dbg = false;
} // namespace mydef
using namespace mydef;
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
//#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define asn ans

string S;

bool check(int d) {
  bool flag[2];
  flag[0] = 1;
  flag[1] = 1;

  for (int i = 0; i < 2; i++) {
    int low, high;
    if (i == 0) {
      low = 0;
      high = (d / 2) * 2;
    } else {
      low = 1;
      high = ((d - 1) / 2) * 2 + 1;
    }

    for (auto &c : S) {
      if (c == '?') {
        if (high == 0) {
          low = 1;
          high = 1;
        } else if (low == d) {
          low = d - 1;
          high = d - 1;
        } else {
          if (low == 0) {
            low = 1;
          } else {
            low--;
          }
          if (high == d)
            high--;
          else {
            high++;
          }
        }
      } else if (c == '0') {
        if (high == 0) {
          flag[i] = false;
          break;
        }
        high--;
        if (low == 0)
          low = 1;
        else
          low--;
      } else if (c == '1') {
        if (low == d) {
          flag[i] = false;
          break;
        }
        low++;
        if (high == d)
          high--;
        else
          high++;
      }
      if (low > high) {
        flag[i] = false;
        break;
      }
      // cerr << low << " " << high << endl;
    }
  }

  return flag[0] | flag[1];
}

void solve() {
  check(1);

  int ok = 1000001;
  int ng = 0;
  while (abs(ok - ng) > 1) {
    int mid = (ok + ng) / 2;
    if (check(mid)) {
      ok = mid;
    } else {
      ng = mid;
    }
  }
  cout << ok << endl;
}

signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cin >> S;
  solve();
  return 0;
}


Measured memory_bytes: 4260