#include <bits/stdc++.h>                                           
 
//#define int long long
//#pragma GCC optimize("Ofast")
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
 
 
#define file(s) freopen(s".in","r",stdin); freopen(s".out","w",stdout);
#define all(x) x.begin(), x.end()
#define sz(s) (int)s.size()
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define s second
#define f first
 
 
using namespace std;
 
 
typedef pair < long long, long long > pll;    
typedef pair < int, int > pii;
typedef unsigned long long ull;         
typedef vector < pii > vpii;
typedef vector < int > vi;
typedef long double ldb;  
typedef long long ll;  
typedef double db;                             
 
 
const int dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1}, block = 555;
const pii base = mp(1171, 3307), Mod = mp(1e9 + 7, 1e9 + 9);
const int inf = 1e9, maxn = 4e5 + 148, mod = 1e9 + 7, N = 1e6 + 21;
const db eps = 1e-12, pi = 3.14159265359;
const ll INF = 1e18;
 
int n;
char s[N], t[N];
deque < int > q;


bool check (int len) {
	while (sz(q)) 
		q.ppb();

	int bal = 0;
	for (int i = 1; i <= n; ++i) {
		if (s[i] == '0')
			--bal;
		else
			++bal;

		t[i] = s[i];

		if (s[i] == '?') {
			t[i] = '1';
			q.pb(i);
		}

		if (bal < 0) {
			bal = 0;
			while (sz(q))
				q.ppb();
		}

		while (bal > len && sz(q)) {
			t[q.back()] = '0';
			q.ppb();
			bal -= 2;
		}

		if (bal > len) 
			return 0;
	}

	bal = 0;
	for (int i = 1; i <= n; ++i) {
		if (t[i] == '0')
			++bal;
		else
			--bal;

		if (bal > len)
			return 0;
		if (bal < 0)
			bal = 0;
	}

	return 1;
}
 
main () {
	scanf("%s", (s + 1));
	n = strlen(s + 1);

	int l = 0, r = n, res = n;
	while (l <= r) {
		int mid = (l + r) >> 1;
		if (check(mid)) {
			res = mid;
			r = mid - 1;
		} else
			l = mid + 1;
	}	
	printf("%d", res);
}