DeveloperOC

#include <iostream>
#include <string>
using namespace std;

string serial;

int main() {
  cin >> serial;

  int size = serial.size();
  int mul3 = false;
  int ans = 0;
  bool targetMul3 = false;
  bool checkSign = true;
  for (int i = 0; i < size - 1; ++i) {

    if (serial[i] == '*') {
      targetMul3 = mul3;
      mul3 = !mul3;
      checkSign = false;
      continue;
    }
    int val = serial[i] - '0';

    if (mul3)
      ans += val * 3;
    else
      ans += val;

    mul3 = !mul3;
  }

  int ret = 0;
  if (checkSign)
    ret = (10 - (ans % 10)) % 10;
  else {
    ret = (10 - (serial[size - 1] - '0')) % 10;

    int mul = targetMul3 ? 3 : 1;
    for (int i = 0; i <= 9; ++i) {
      if (ret == ((i * mul) + ans) % 10) {
        ret = i;
        break;
      }
    }
  }

  cout << ret;
  return 0;
}