//#define _GLIBCXX_DEBUG

#include<bits/stdc++.h>
using namespace std;

#define endl '\n'
#define lfs cout<<fixed<<setprecision(10)
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define fi first
#define se second
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define EB emplace_back
#define rep(i,n,m) for(ll i = (n); i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = (ll)(m) - 1; i >= (ll)(n); i--)
using ll = long long;
using ld = long double;
const ll MOD1 = 1e9+7;
const ll MOD9 = 998244353;
const ll INF = 1e18;
using P = pair<ll, ll>;
template<typename T1, typename T2>
bool chmin(T1 &a,T2 b){if(a>b){a=b;return true;}else return false;}
template<typename T1, typename T2>
bool chmax(T1 &a,T2 b){if(a<b){a=b;return true;}else return false;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>
void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>
void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>&v,ll h,ll w){for(ll i=0;i<h;i++)
{for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>
void debug(vector<T>&v,ll n){if(n!=0)cout<<v[0];
for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>
vector<vector<T>>vec(ll x, ll y, T w){
  vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
vector<ll>dx={1,-1,0,0,1,1,-1,-1};
vector<ll>dy={0,0,1,-1,1,-1,1,-1};
template<typename T>
vector<T> make_v(size_t a,T b){return vector<T>(a,b);}
template<typename... Ts>
auto make_v(size_t a,Ts... ts){
  return vector<decltype(make_v(ts...))>(a,make_v(ts...));
}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2>&p){
  return os << p.first << " " << p.second;
}
//mt19937 mt(chrono::steady_clock::now().time_since_epoch().count());

bool solve(string &s,ll lim){
  vector<P>p(1,MP(0,0));
  ll n=s.size();
  rep(i,0,n){
    vector<P>tmp;
    for(auto z:p){
      if(s[i]!='1')tmp.EB(z.fi+1,max(0LL,z.se-1));
      if(s[i]!='0')tmp.EB(max(0LL,z.fi+-1),z.se+1);
    }
    ll sz=tmp.size();
    /*vector<bool>t(sz,true);
    rep(i,0,sz)if(max(tmp[i].fi,tmp[i].se)>lim)t[i]=false;
    rep(i,0,sz)rep(j,i+1,sz){
      if(tmp[i].fi>=tmp[j].fi&&tmp[i].se>=tmp[j].se)t[j]=false;
      if(tmp[i].fi<=tmp[j].fi&&tmp[i].se<=tmp[j].se&&tmp[i]!=tmp[j])t[i]=false;
    }*/
    //debug(tmp,sz);
    p.clear();
    sort(ALL(tmp));
    //debug(tmp,sz);
    rep(i,0,sz)if(max(tmp[i].fi,tmp[i].se)<=lim){
      if(p.empty()||p.back().se>tmp[i].se)p.EB(tmp[i]);
    }
    //debug(p,p.size());
    /*rep(i,0,p.size()){
      cout<<p[i]<<"|";
    }*/
    //cout<<endl;
    //cout<<p.size()<<endl;
    if(p.empty())return false;
  }
  return !p.empty();
}
int main(){
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  ll res=0,buf=0;
  bool judge = true;
  string s;cin>>s;
  ll n=s.size();
  ll ok=n,ng=0;
  solve(s,n);
  /*while(ok-ng>=2){
    ll mid=(ok+ng)/2;
    if(solve(s,mid))ok=mid;
    else ng=mid;
  }*/
  cout<<ok<<endl;
  return 0;
}