#include <bits/stdc++.h>
//    #include <boost/multiprecision/cpp_int.hpp>
  //  using namespace boost::multiprecision;
 #define int  long long
 #define inf  1000000007
 #define pa pair<int,int>
 #define ll long long
 #define pal pair<double,double>
  #define PI 3.14159265358979323846
  #define  mp make_pair
  #define  pb push_back
  #define EPS (1e-8)
                                          
    int dx[8]={0,1,0,-1,1,1,-1,-1};
    int dy[8]={1,0,-1,0,-1,1,1,-1};
                                            using namespace std;
                                   			class pa3{
                                            	public:
                                            	int x;
                                   				int y,z;
                                            	pa3(int x=0,int y=0,int z=0):x(x),y(y),z(z) {}
                                            	bool operator < (const pa3 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		 return z<p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                   				bool operator > (const pa3 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		 return z>p.z;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa3 &p) const{
                                            		return x==p.x && y==p.y && z==p.z;
                                            	}
                                            		bool operator != (const pa3 &p) const{
                                            			return !( x==p.x && y==p.y && z==p.z);
                                            	}
                                            
                                            };
                                            
                                            class pa4{
                                            	public:
                                            	int x;
                                            	int y,z,w;
                                            	pa4(int x=0,int y=0,int z=0,int w=0):x(x),y(y),z(z),w(w) {}
                                            	bool operator < (const pa4 &p) const{
                                            		if(x!=p.x) return x<p.x;
                                            		if(y!=p.y) return y<p.y;
                                            		if(z!=p.z)return z<p.z;
                                            		return w<p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator > (const pa4 &p) const{
                                            		if(x!=p.x) return x>p.x;
                                            		if(y!=p.y) return y>p.y;
                                            		if(z!=p.z)return z>p.z;
                                            		return w>p.w;
                                            		//return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa4 &p) const{
                                            		return x==p.x && y==p.y && z==p.z &&w==p.w;
                                            	}
                                            		
                                            
                                            };
                                            class pa2{
                                            	public:
                                            	int x,y;
                                            	pa2(int x=0,int y=0):x(x),y(y) {}
                                            	pa2 operator + (pa2 p) {return pa2(x+p.x,y+p.y);}
                                            	pa2 operator - (pa2 p) {return pa2(x-p.x,y-p.y);}
                                            	bool operator < (const pa2 &p) const{
                                            		return y != p.y ? y<p.y: x<p.x;
                                            	}
                                            	bool operator > (const pa2 &p) const{
                                            		return x != p.x ? x<p.x: y<p.y;
                                            	}
                                            	bool operator == (const pa2 &p) const{
                                            		return abs(x-p.x)==0 && abs(y-p.y)==0;
                                            	}
                                            	bool operator != (const pa2 &p) const{
                                            		return !(abs(x-p.x)==0 && abs(y-p.y)==0);
                                            	}
                                            		
                                            
                                            };
                                            
 
                      
                                string itos( int i ) {
                                ostringstream s ;
                                s << i ;
                                return s.str() ;
                                }
                                 
                                int Gcd(int v,int b){
                                	if(v==0) return b;
                                	if(b==0) return v;
                                	if(v>b) return Gcd(b,v);
                                	if(v==b) return b;
                                	if(b%v==0) return v;
                                	return Gcd(v,b%v);
                                }
                 
                            
                                int mod;
int extgcd(int a, int b, int &x, int &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    int d = extgcd(b, a%b, y, x);
    y -= a/b * x;
    return d;
}
pa operator+(const pa & l,const pa & r) {   
    return {l.first+r.first,l.second+r.second};                                    
}    
pa operator-(const pa & l,const pa & r) {   
    return {l.first-r.first,l.second-r.second};                                    
}  
                int beki(int wa,int rr,int warukazu){
                	if(rr==0) return 1%warukazu;
                	if(rr==1) return wa%warukazu;
                	wa%=warukazu;
                	if(rr%2==1) return ((ll)beki(wa,rr-1,warukazu)*(ll)wa)%warukazu;
                	ll zx=beki(wa,rr/2,warukazu);
                	return (zx*zx)%warukazu;
                }
 
                              
                int pr[1000100];
                int inv[1000110];
                

                
    			int comb(int nn,int rr){
    				if(rr<0 || rr>nn || nn<0) return 0;
    				int r=pr[nn]*inv[rr];
    				r%=mod;
    				r*=inv[nn-rr];
    				r%=mod;
    				return r;
    			}
               
                void gya(int ert){
                	pr[0]=1;
                	for(int i=1;i<=ert;i++){
                		pr[i]=((ll)pr[i-1]*i)%mod;
                	}
                		inv[ert]=beki(pr[ert],mod-2,mod);
                	for(int i=ert-1;i>=0;i--){
                		inv[i]=(ll)inv[i+1]*(i+1)%mod;
                	}
                }
               
              //   cin.tie(0);
    		//	ios::sync_with_stdio(false);
    			//priority_queue<pa3,vector<pa3>,greater<pa3>> pq;            
                 //sort(ve.begin(),ve.end(),greater<int>());
 //   mt19937(clock_per_sec);
  //  mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()) ;

string t[2];
int a[2][1000020];
void make_hoge(int r,int n){
	a[r][n]=0;
	int ima=0;
	for(int i=n-1;i>=0;i--){
		if(t[r][i]!='0')ima=max(0ll,ima-1);
		else ima++;
		a[r][i]=ima;
	}
	//for(int i=0;i<=n;i++)cout<<a[r][i];
	//cout<<endl;
}

int sol(int x,int r,int n){
	int ima=0;
	int ma=0;
	//cout<<x<<" "<<r<<endl;
	for(int i=x;i<n;i++){
		if(t[r][i]=='1')ima++;
		else if(t[r][i]=='0')ima--;
		else{
			if(a[r][i+1]<=ima-1)ima--;
			else ima++;
		}
		assert(ima>=0);
		ma=max(ma,ima);
	}
	return ma;
}

pa solve(int r,int n){
	return mp(sol(n-r,1,n),sol(r,0,n));
}

int solve(string s){
	int n=s.length();
	t[0]=s;
	t[1]=s;
	reverse(t[1].begin(),t[1].end());
	for(int i=0;i<n;i++)if(t[1][i]!='?')t[1][i]^=('0'^'1');

	make_hoge(0,n);
	make_hoge(1,n);
	vector<int> ve[2];
	for(int i=0;i<=n;i++)if(a[0][i]+a[1][n-i]==0){
		ve[i%2].pb(i);
	//	cout<<i<<endl;
	}
	int ans=inf;
	for(int r=0;r<2;r++)if(ve[r].size()){
		if(ve[r].size()==1){
			pa z=solve(ve[r][0],n);
			ans=min(ans,max(z.first,z.second));
		}
		else{
			pa z=solve(ve[r][0],n);
			if(z.first-z.second>=0){
				ans=min(ans,z.first);
				continue;
			}
			z=solve(ve[r].back(),n);
			if(z.first-z.second<=0){
				ans=min(ans,z.second);
				continue;
			}
			int si=0,ue=ve[r].size()-1;
			while(ue-si>1){
				int me=(ue+si)/2;
				z=solve(ve[r][me],n);
				if(z.first-z.second<0)si=me;
				else ue=me;
			}
			pa z1=solve(ve[r][si],n),z2=solve(ve[r][ue],n);
			ans=min(ans,max(z1.first,z1.second));
			ans=min(ans,max(z2.first,z2.second));
			
		}
	}
	return ans;
}


signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	string s;
	cin>>s;
	int t1=solve(s);
	cout<<t1<<endl;
	return 0;
	reverse(s.begin(),s.end());
	int t2=solve(s);
	cout<<min(t1,t2)<<endl;
	
	return 0;
 }

Measured memory_bytes: 31580