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

void replaceAll(string &s, string a, string b){
  int pos = 0;
  while((pos=s.find(a))!=string::npos)s.replace(pos,a.size(),b);
}

int toInt(string s){
  stringstream ss(s);
  int res;
  ss >> res;
  return res;
}

int main(){
  int i;
  string s;
  while(cin >> s){
    s.replace(s.find("+"),1," "); s.replace(s.find("="),1," ");

    string t[3];
    stringstream ss(s);
    for(i=0;i<3;i++)ss >> t[i];

    for(i=0;i<10;i++){
      if(i==0){
	bool f = false;
	for(int j=0;j<3;j++)
	  if(t[j][0] == 'X')f = true;
	if(f)continue;
      }

      string tmp[3];
      for(int j=0;j<3;j++)tmp[j] = t[j];

      string digit = "";
      digit += '0'+i;
      for(int j=0;j<3;j++)replaceAll(tmp[j],"X",digit);
      if(toInt(tmp[0]) + toInt(tmp[1]) == toInt(tmp[2])){
	cout << i << endl;
	break;
      }
    }
    if(i==10)cout << "NA\n";
  } 
}