#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  string s; cin >> s;
  int n = s.length(), lb = 0, ub = n;
  while (ub - lb > 1) {
    int mid = (lb + ub) >> 1;
    bool ok = false;
    for (int parity : {0, 1}) {
      int l = parity, r = mid - (mid % 2 != parity);
      for (char c : s) {
        if (l > r) break;
        if (c == '0') {
          --l; --r;
          if (l < 0) l += 2;
        } else if (c == '1') {
          ++l; ++r;
          if (r > mid) r -= 2;
        } else if (c == '?') {
          --l; ++r;
          if (l < 0) l += 2;
          if (r > mid) r -= 2;
        }
      }
      ok |= l <= r;
    }
    (ok ? ub : lb) = mid;
  }
  cout << ub << '\n';
  return 0;
}
