#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

string in;
vector<string> V;

string change(string a, int j){
  for(int i = 0; i < a.length(); i++) 
    if(a[i] == 'X') a[i] = j+'0';
  return a;
}

string p(string a, string b){
  if(a.length() < b.length()) swap(a,b);
  int diff = a.length() - b.length();
  reverse(a.begin(),a.end());
  reverse(b.begin(),b.end());
  for(int i = 0; i < diff; i++) b+="0";
  int status = 0;
  for(int i = 0; i < a.length(); i++){
    if(status){
      a[i]++;
      status = 0;
    }
    if(a[i]+(b[i]-'0') > '9'){
      a[i] += (b[i]-'0')-10;
      status = 1;
    }
    else a[i] += b[i]-'0';
  }
  if(status) a+="1";
  reverse(a.begin(),a.end());
  return a;
}

int check(string a,string b,string c,int num){
  string ans = p(a,b);
  //cout << ans << " " << c << endl;
  if(ans == c){
    cout << num << endl;
    return 1;
  }
  return 0;
}


int where_X(){
  for(int i = 0; i < V.size(); i++){
    string s = V[i];
    if(s[0] == 'X' && s.length() > 1) return 1;
  }
  return 0;
}
void solve(){
  string s[3];
  int start = where_X();
  for(int i = start; i < 10; i++){
    for(int j = 0; j < 3; j++) s[j] = change(V[j],i); 
    if(check(s[0],s[1],s[2],i)) break;
    if(i == 9) cout << "NA" << endl;
  }
}

int main(){
  while(cin >> in){
    V.clear();
    in += '+';
    string out = "";
    for(int i = 0; i < in.length(); i++){
      if(in[i] == '+' || in[i] == '='){
	V.push_back(out);
	out = "";
      }else out += in[i];
    }
    solve();
  }
  return 0;
}