#include<iostream>
#include<string>
#include<algorithm>
using namespace std;

int main(){
	string s,a,b,c;
	while(cin>>s){
		int p,e;
		p=s.find('+',0);
		e=s.find('=',p);
		a=s.substr(0,p);
		b=s.substr(p+1,e-p-1);
		c=s.substr(e+1);
		int lz=(1<a.size()&&a[0]=='X'||1<b.size()&&b[0]=='X'||1<c.size()&&c[0]=='X');
		reverse(a.begin(),a.end());
		reverse(b.begin(),b.end());
		reverse(c.begin(),c.end());
		int ans;
		for(int i=lz;i<10;i++){
			int carry=0;
			ans=i;
			for(int j=0;j<126;j++){
				int x,y,z;
				x=a.size()<=j?0:a[j]=='X'?i:a[j]-'0';
				y=b.size()<=j?0:b[j]=='X'?i:b[j]-'0';
				z=c.size()<=j?0:c[j]=='X'?i:c[j]-'0';
				if((x+y+carry)%10!=z){
					ans=-1;
					break;
				}
				carry=(x+y+carry)/10;
			}
			if(ans!=-1)break;
		}
		if(ans==-1)cout<<"NA"<<endl;
		else cout<<ans<<endl;
	}
	return 0;
}