#include<bits/stdc++.h>
using namespace std;
typedef long long int lld;

int main(){
  string str;
  while(cin >> str){
    string num[3] = {"","",""};
    int idx = 0;
    for(int i=0;i<str.size();i++){
      if(str[i] == '+' || str[i] == '=') idx++;
      else {
	num[idx] += str[i];
      }
    }
    int l1=num[0].size(),l2=num[1].size();
    if(l1<l2)swap(l1,l2),swap(num[0],num[1]);
    int flg = false;
    for(char c='0';c<='9';c++){
      if(c == '0'){
	if(num[0].size() > 1 && num[0][0] == 'X') continue;
	if(num[1].size() > 1 && num[1][0] == 'X') continue;
	if(num[2].size() > 1 && num[2][0] == 'X') continue;
      }
      string tmp[3] = {"","",""};
      for(int i=0;i<3;i++){
	for(int j=0;j<num[i].size();j++){
	  if(num[i][j] == 'X') tmp[i] += c;
	  else tmp[i] += num[i][j];
	}
      }
      for(int i=l1-1,j=l2-1;i>=0;i--,j--){
	if(j>=0) tmp[0][i]+=tmp[1][j]-'0';
	if(tmp[0][i]>'9'){
	  tmp[0][i]-=10;
	  if(i==0)tmp[0]="1"+tmp[0];
	  else tmp[0][i-1]++;
	}
      }
      if(tmp[0] == tmp[2]){
	cout << c << endl;
	flg = true;
	break;
      }
    }
    if(!flg) cout << "NA" << endl;
  }
}