#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;
int main(void){
  string s;
  while(getline(cin,s)){
  	int NA=1;
    for(int i=0;i<10;++i){
      string tmp=s;
      for(int j=0;j<tmp.size();++j) if(tmp[j]=='X') tmp[j]='0'+i;
      char a[125],b[125],c[125];
      sscanf(tmp.c_str(),"%[^+]%*c%[^=]%*c%s",a,b,c);
      string sa(a),sb(b),sc(c),res;
      reverse(sa.begin(),sa.end());
      reverse(sb.begin(),sb.end());
      reverse(sc.begin(),sc.end());
      for(int k=0,sum,carry=0;k<((sa.size()<sb.size())?sb.size()+1:sa.size()+1);++k){
      	if(sa.size()>k&&sb.size()>k){
	      	sum=(sa[k]-'0'+sb[k]-'0'+carry)%10;
	      	carry=(sa[k]-'0'+sb[k]-'0'+carry)/10;
	      	res+=(char)(sum+'0');
      	}else{
      		if(k<sa.size()||k<sb.size()){
      			int tmp=(sa.size()>sb.size())?sa[k]-'0':sb[k]-'0';
      			sum=(tmp+carry)%10;
      			carry=(tmp+carry)/10;
      			res+=(char)(sum+'0');
      		}
      		if(sa.size()<=k&&sb.size()<=k&&carry){
      			res+=carry+'0';
      			carry=0;
      		}
      	}
      }
      if(res==sc){NA=0;cout<<i<<endl;break;}
    }
    if(NA)cout<<"NA"<<endl;
  }
}