#include <bits/stdc++.h>
namespace IO {
static const int IN_BUF = 1 << 23, OUT_BUF = 1 << 23;
inline char myGetchar() {
  static char buf[IN_BUF], *ps = buf, *pt = buf;
  if (ps == pt) {
    ps = buf, pt = buf + fread(buf, 1, IN_BUF, stdin);
  }
  return ps == pt ? EOF : *ps++;
}
template <typename T>
inline bool read(T &x) {
  bool op = 0;
  char ch = IO::myGetchar();
  x = 0;
  for (; !isdigit(ch) && ch != EOF; ch = IO::myGetchar()) {
    op ^= (ch == '-');
  }
  if (ch == EOF) {
    return false;
  }
  for (; isdigit(ch); ch = IO::myGetchar()) {
    x = x * 10 + (ch ^ '0');
  }
  if (op) {
    x = -x;
  }
  return true;
}
inline int readStr(char *s) {
  int n = 0;
  char ch = IO::myGetchar();
  for (; isspace(ch) && ch != EOF; ch = IO::myGetchar())
    ;
  for (; !isspace(ch) && ch != EOF; ch = IO::myGetchar()) {
    s[n++] = ch;
  }
  s[n] = '\0';
  return n;
}
inline void myPutchar(char x) {
  static char pbuf[OUT_BUF], *pp = pbuf;
  struct _flusher {
    ~_flusher() { fwrite(pbuf, 1, pp - pbuf, stdout); }
  };
  static _flusher outputFlusher;
  if (pp == pbuf + OUT_BUF) {
    fwrite(pbuf, 1, OUT_BUF, stdout);
    pp = pbuf;
  }
  *pp++ = x;
}
template <typename T>
inline void print_(T x) {
  if (x == 0) {
    IO::myPutchar('0');
    return;
  }
  static int num[40];
  if (x < 0) {
    IO::myPutchar('-');
    x = -x;
  }
  for (*num = 0; x; x /= 10) {
    num[++*num] = x % 10;
  }
  while (*num) {
    IO::myPutchar(num[*num] ^ '0');
    --*num;
  }
}
template <typename T>
inline void print(T x, char ch = '\n') {
  print_(x);
  IO::myPutchar(ch);
}
inline void printStr_(const char *s, int n = -1) {
  if (n == -1) {
    n = strlen(s);
  }
  for (int i = 0; i < n; ++i) {
    IO::myPutchar(s[i]);
  }
}
inline void printStr(const char *s, int n = -1, char ch = '\n') {
  printStr_(s, n);
  IO::myPutchar(ch);
}
}  // namespace IO
using namespace IO;
const int N = 1000005;
int n;
char a[N];
int sum[N], suf[N];
int solve(int mn) {
  int mx = 0, d = 0;
  for (int i = 1; i <= n; ++i) {
    if (a[i] == '?' && suf[i] - d - 2 >= mn) {
      d += 2;
    }
    mx = std::max(mx, sum[i] - d);
  }
  return mx - mn;
}
int main() {
  n = readStr(a + 1);
  for (int i = 1; i <= n; ++i) {
    sum[i] = sum[i - 1] + (a[i] == '0' ? -1 : 1);
  }
  suf[n] = sum[n];
  for (int i = n - 1; i; --i) {
    suf[i] = std::min(suf[i + 1], sum[i]);
  }
  print(std::min(solve(suf[1]), solve(suf[1] - 1)));
}
