#include <bits/stdc++.h>
using namespace std;
const int P = 1e9 + 7, INF = 0x3f3f3f3f;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long qpow(long long a, long long n) {
  long long r = 1 % P;
  for (a %= P; n; a = a * a % P, n >>= 1)
    if (n & 1) r = r * a % P;
  return r;
}
long long inv(long long first) {
  return first <= 1 ? 1 : inv(P % first) * (P - P / first) % P;
}
inline int rd() {
  int first = 0;
  char p = getchar();
  while (p < '0' || p > '9') p = getchar();
  while (p >= '0' && p <= '9') first = first * 10 + p - '0', p = getchar();
  return first;
}
const int N = 1e6 + 50;
char s[N];
int n;
int chk(int first) {
  for (int k = 0; k <= 1; ++k) {
    int a = k, b = first;
    if (a % 2 != b % 2) --b;
    for (int i = 1; i <= n; ++i) {
      if (s[i] == '0')
        --a, --b;
      else if (s[i] == '1')
        ++a, ++b;
      else
        --a, ++b;
      if (a < 0) a += 2;
      if (b > first) b -= 2;
      if (b < a) break;
      if (i == n) return 1;
    }
  }
  return 0;
}
int main() {
  scanf("%s", s + 1);
  int l = 0, r = n = strlen(s + 1), ans;
  while (l <= r) {
    if (chk(((l + r) >> 1)))
      ans = ((l + r) >> 1), r = ((l + r) >> 1) - 1;
    else
      l = ((l + r) >> 1) + 1;
  }
  printf("%d\n", ans);
}
