#include <iostream>
#include <algorithm>
#include <string>
#include <sstream>

using namespace std;

void change(string &s,int num){
  int length = (int)s.size();
  char ch = num + '0';

  for(int i = 0 ; i < length ; i++){
    if(s[i] == 'X'){
      s[i] = ch;
    }
  }
}

bool check(char ch,int size){
  if(ch == 'X' && size > 1) return true;
  return false;
}

string sum(string a,string b){
  string res;
  stringstream ax,by,cz;
  int x,y,z;

  ax << a; by << b;
  ax >> x; by >> y;

  z = x + y;
  cz << z; cz >> res;

  return res;
}

int main(){
  string str;

  while(cin >> str){
    int pos_plus = str.find('+'),pos_equal = str.find('=');
    
    string x = str.substr(0,pos_plus);
    string y = str.substr(pos_plus+1,pos_equal-pos_plus-1);
    string z = str.substr(pos_equal + 1);

    int start = 0;
    if(check(x[0],x.size()) || 
       check(y[0],y.size()) || 
       check(z[0],z.size())) {

      start++;

    }   
 
    int ans;
    bool found = false;
    for(int i = start ; i < 10 ; i++){
      string a = x, b = y, c = z;
   
      change(a,i); change(b,i); change(c,i);
      if(sum(a,b) == c){
	found = true;
	ans = i;
	break;
      }
    }

    if(found) cout << ans << endl;
    else cout << "NA" << endl;
  }

  return 0;
}