/*/ Author: kal013 /*/
// #pragma GCC optimize ("O3")
#include "bits/stdc++.h"
#include "ext/pb_ds/assoc_container.hpp"
#include "ext/pb_ds/tree_policy.hpp"
using namespace std;
using namespace __gnu_pbds;

template<class T> 
using ordered_set = tree<T, null_type,less<T>, rb_tree_tag,tree_order_statistics_node_update> ;

template<class key, class value, class cmp = std::less<key>>
using ordered_map = tree<key, value, cmp, rb_tree_tag, tree_order_statistics_node_update>;
// find_by_order(k)  returns iterator to kth element starting from 0;
// order_of_key(k) returns count of elements strictly smaller than k;

struct custom_hash { // Credits: https://codeforces.com/blog/entry/62393
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};

template<class T> ostream& operator<<(ostream &os, vector<T> V) {
    os << "[ ";
    for(auto v : V) os << v << " ";
    return os << "]";
}
template<class T> ostream& operator<<(ostream &os, set<T> S){
    os << "{ ";
    for(auto s:S) os<<s<<" ";
    return os<<"}";
}
template<class T> ostream& operator<<(ostream &os, unordered_set<T> S){
    os << "{ ";
    for(auto s:S) os<<s<<" ";
    return os<<"}";
}
template<class T> ostream& operator<<(ostream &os, ordered_set<T> S){
    os << "{ ";
    for(auto s:S) os<<s<<" ";
    return os<<"}";
}
template<class L, class R> ostream& operator<<(ostream &os, pair<L,R> P) {
    return os << "(" << P.first << "," << P.second << ")";
}
template<class L, class R> ostream& operator<<(ostream &os, map<L,R> M) {
    os << "{ ";
    for(auto m:M) os<<"("<<m.first<<":"<<m.second<<") ";
    return os<<"}";
}
template<class L, class R> ostream& operator<<(ostream &os, unordered_map<L,R> M) {
    os << "{ ";
    for(auto m:M) os<<"("<<m.first<<":"<<m.second<<") ";
    return os<<"}";
}
template<class L, class R, class chash = std::hash<R> > ostream& operator<<(ostream &os, gp_hash_table<L,R,chash> M) {
    os << "{ ";
    for(auto m:M) os<<"("<<m.first<<":"<<m.second<<") ";
    return os<<"}";
}

#define TRACE
#ifdef TRACE
    #define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
    template <typename Arg1>
    void __f(const char* name, Arg1&& arg1){
        cerr << name << " : " << arg1 << endl;
    }
    template <typename Arg1, typename... Args>
    void __f(const char* names, Arg1&& arg1, Args&&... args){
        const char* comma = strchr(names + 1, ',');
        cerr.write(names, comma - names) << " : " << arg1<<" | ";
        __f(comma+1, args...);
    }
#else
    #define trace(...) 1
#endif

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

inline int64_t random_long(long long l,long long r){
    uniform_int_distribution<int64_t> generator(l,r);
    return generator(rng);
}
inline int64_t random_long(){
    uniform_int_distribution<int64_t> generator(LLONG_MIN,LLONG_MAX);
    return generator(rng);
}


/*/---------------------------Defines----------------------/*/
typedef vector<int> vi;
typedef pair<int,int> pii;

#define ll long long
#define F first
#define S second
#define pb push_back
#define endl "\n"
#define all(v) (v).begin(),(v).end()
/*/-----------------------Modular Arithmetic---------------/*/

const int mod=1e9+7;
inline int add(int x,int y){
    x+=y;
    if (x>=mod) return x-mod;
    return x;
}
inline int sub(int x,int y){
    x-=y;
    if (x<0) return x+mod;
    return x;
}
inline int mul(int x,int y){
    return (x*1ll*y)%mod;
}
inline int power(int x,int y){
    int ans=1;
    while(y){
        if (y&1) ans=mul(ans,x);
        x=mul(x,x);
        y>>=1;
    }
    return ans;
}
inline int inv(int x){
    return power(x,mod-2);
}
/*/-----------------------------Code begins----------------------------------/*/

const int N = 1e6 + 100;
int pref[N],v[N],k[N],K[N],suf_k[N];


inline int min_max(int n,int m){

	for(int i = 0; i<=n; ++i){
		k[i] = (pref[i] + v[i] - m) / 2;
	}
	suf_k[n] = k[n];

	for(int i = n-1 ;i >= 0 ; --i){
		suf_k[i] = min(suf_k[i+1],k[i]);
	}


	// Kz is the number of positions that will be -1 in [1..z].
	// kz is the number of positions that will be -1 in [1..z] only taking m into consideration.
	// Kz = min( k z..n, K[z-1] + v[z] - v[z-1], v[z])
	// ans = max (pref[z] + v[z] - 2*K[z])

	// m -> (m-2)  ---> k'z <= k[z] + 1  ----> K'z <= K[z] + 1 ----> ans' >= ans - 2 
	// difference would be same or increase 
	int ans = 0;
	for(int i = 0; i<=n; ++i){
		K[i] = min(suf_k[i],v[i]);
		if ( i > 0){
			K[i] = min(K[i-1] + v[i] - v[i-1],K[i]);
		}

		assert(pref[i] + v[i] - 2*K[i] >= m);
		ans = max(ans, pref[i] + v[i] - 2*K[i]);
	}
	return ans;
}

void solve(){
    string s;
    cin>>s;

    pref[0] = 0;
    v[0] = 0;

    int n = s.size();

    int m = 0;
    int curr_pref = 0;
    for(int i = 1; i<=n; ++i){
    	if (s[i-1] == '0'){
    		pref[i] = pref[i-1] - 1;
    		v[i] = v[i-1];
    	}
    	else if (s[i-1] == '1'){
    		pref[i] = pref[i-1] + 1;
    		v[i] = v[i-1];
    	}
    	else{
    		pref[i] = pref[i-1];
    		v[i] = v[i-1] + 1;
    	}

    	m = min(m,pref[i] + v[i]);
    }
    int ans = min(min_max(n,m) - m,min_max(n,m-1) - m + 1 );

    cout<<ans<<endl;




}
int main(){
    // Use "set_name".max_load_factor(0.25);"set_name".reserve(512); with unordered set
    // Or use gp_hash_table<X,null_type>
    ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
    cout<<fixed<<setprecision(25);
    int t=1;
    // cin>>t;
    while(t--) {
        solve();
    }
}




Measured memory_bytes: 23820