#include<iostream>
#include<string>
#include<sstream>
#include<algorithm>
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);
}

string add(string a,string b){
  if(a.size() < b.size())return add(b,a);

  reverse(a.begin(),a.end());
  reverse(b.begin(),b.end());

  int carry = 0;
  for(int i=0;i<a.size();i++){
    a[i] += carry;
    if(i<b.size())a[i] += b[i] - '0';
    if(a[i] > '9'){
      carry = 1;
      a[i] -= 10;
    }else carry = 0;
  }
  
  if(carry)a += "1";
  reverse(a.begin(),a.end());
  return a;
}

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' && t[j].size()>1)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(add(tmp[0],tmp[1])==tmp[2]){
	cout << i << endl;
	break;
      }
    }
    if(i==10)cout << "NA\n";
  } 
}