#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

string calc(string s1, string s2){
  string res;
  int n = max(s1.size(), s2.size());
  while(s1.size() < n) s1 = '0' + s1;
  while(s2.size() < n) s2 = '0' + s2;
  //   cout << "s1 = " << s1 << endl;
  //cout << "s2 = " << s2 << endl;
  int c = 0;
  for(int i = n-1 ; i >= 0 ; i--){
    char ch = ((s1[i]-'0')+(s2[i]-'0')+c)%10 + '0';
    c = ((s1[i]-'0')+(s2[i]-'0')+c)/10;
    res += ch;
  }
  if(c) res += c+'0';
  reverse(res.begin(), res.end());
  while(res.size() > 1 && res[0] == '0') res.erase(res.begin());
  //cout << res << endl;
  return res;
}

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

int main(){    
  string op;
  while(cin >> op){  
    bool flag = false;
    for(char ii = '0' ; ii <= '9' ; ii++){
      string left1, left2, right;
      int index1, index2;
      index1 = op.find("+");
      index2 = op.find("=");
      left1 = op.substr(0, index1);
      left2 = op.substr(index1+1, index2-index1-1);
      right = op.substr(index2+1);
      
      left1 = convert(left1, ii);
      left2 = convert(left2, ii);
      right = convert(right, ii);
      
      if(left1.size() > 1 && left1[0] == '0' ||
	 left2.size() > 1 && left2[0] == '0' ||
	 right.size() > 1 && right[0] == '0') continue;
      
      //      while(left1.size() > 1 && left1[0] == '0') left1.erase(left1.begin());  
      //while(left2.size() > 1 && left2[0] == '0') left2.erase(left2.begin());  
      //     while(right.size() > 1 && right[0] == '0') right.erase(right.begin());
      //cout << left1 << '+' << left2 << '=' << right << endl;
            
      if(calc(left1, left2) == right){
	//cout << left1 << '+' << left2 << '=' << right << endl;
	cout << ii << endl;
	flag = true;
	break;
      }
    }
    if(!flag) cout << "NA" << endl;
  }
  return 0;
}
    