#include <stdio.h>
#include <iostream>
#include <string>

using namespace std;

#define MAXNUM 128
int npow(int a, int n){
  if(n == 0) return 1;
  else return a * npow(a, n-1);
}

bool is_num(char c){
  if( c >= '0' && c <= '9') return true;
  else return false;
}
int main(void){
  int c = 0;

  while(true){
    string buf[3];

    if(c == EOF) break;
    for(int j = 0; j < 3; j++){
      for(int i = 0; i < MAXNUM; i++){
        c = getchar();
        if(c == EOF) goto END;
        if(c == '+' || c == '=' || c == '\n')
          break;
        buf[j].push_back(c);
      }
    }
    int x = 0;
    for(int j = 0; j < 3; j++){
      if(buf[j][0] == 'X') {
        x = 1;
        break;
      }
    }
    for(; x <= 9; x++){
      int num[3] = {0, 0, 0};
      for(int j = 0; j < 3; j++){
        int lngth = buf[j].length();
        for(int i = 0; i < lngth; i++){
          if(buf[j][i] == 'X') num[j] += x * npow(10, lngth-1-i);
          else num[j] += (buf[j][i]-'0') * npow(10, lngth-1-i);
        }
      }
      if(num[0] + num[1] == num[2]){
        break;
      }
    }
    if(x == 10) cout << "NA" << endl;
    else cout << x << endl;
  }
END:
  return 0;
}