#include<iostream>
#include<string>
#include<cstring>
#include<vector>
#include<set>
#include<cmath>
using namespace std;
typedef vector<int> vi;

string plus_string(string a,string b)
{
  string c;
  reverse(a.begin(),a.end());
  reverse(b.begin(),b.end());
  while(a.size()!=b.size())
    {
      if(a.size()<b.size())
	{
	  a.push_back('0');
	}
      else
	{
	  b.push_back('0');
	}
    }
  for(int i=0;i<(int)a.size();i++)
    {
      c.push_back('0');
    }
  int n=0;
  for(int i=0;i<a.size();i++)
    {
      if(n+(a[i]-'0')+(b[i]-'0')<=9)
	{
	  c[i]=a[i]+b[i]-'0'+n;
	  n=0;
	}
      else
	{
	  c[i]=a[i]+b[i]-'0'-10+n;
	  n=1;
	}
    }
  if(n==1)
    {
      c.push_back('1');
    }
  reverse(c.begin(),c.end());
  return c;
}

string change_x(string s,char c)
{
  for(int i=0;i<(int)s.size();i++)
    {
      if(s[i]=='X') s[i]=c;
    }
  return s;
}

int main()
{
  string s;
  string num1="",num2="";
  string ans="";
  string a,b,c;
  int plus,equal;
  bool clear;
  while(cin >> s)
    {
      clear=false;
      for(int i=0;i<(int)s.size();i++)
	{
	  if(s[i]=='+') plus=i;
	  else if(s[i]=='=') equal=i;
	}
      num1=s.substr(0,plus);
      num2=s.substr(plus+1,equal-plus-1);
      ans=s.substr(equal+1);
      for(int i=0;i<=9;i++)
	{
	  a=change_x(num1,i+'0');
	  b=change_x(num2,i+'0');
	  c=change_x(ans,i+'0');
	  if(plus_string(a,b)==c)
	    {
	      cout << i << endl;
	      clear=true;
	    }
	}
      if(!clear)cout << "NA" << endl;
    }
  return 0;
}

