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

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;
}

char calc(char x,char y,char z,bool &C){
  int a = x - '0',b = y - '0',c = z - '0';
  int d = a + b + c;

  if(d >= 10){
    C = true;
    d -= 10;
  }

  return d + '0';
}

string sum(string a,string b){
  string res = "";

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

  int length;
  if((int)a.size() > (int)b.size()){
    length = (int)a.size();
    
    for(int i = (int)b.size() ; i < length ; i++){
      b += '0';
    }

  }
  else{
    length = (int)b.size();

    for(int i = (int)a.size() ; i < length ; i++){
      a += '0';
    }

  }

  for(int i = 0 ; i <= length ; i++)
    res += '0';

  for(int i = 0 ; i < length ; i++){
    bool C = false;
    res[i] = calc(a[i],b[i],res[i],C);
    if(C) res[i+1] = ((res[i+1]-'0') + 1) + '0';
  }

  for(int i = length ;; i--){
    
    if(res[i] == '0'){
      res.erase(res.begin()+i);
    }
    else{
      break;
    }
    
  }

  reverse(res.begin(),res.end());  

  return res;
}

int main(){
  string str;

  while(cin >> str){
    if(str == "X+X=X"){
      cout << "0" << endl;
      continue;
    }

    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 = 1;

    }    

    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;
}