#define _USE_MATH_DEFINES
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>


using namespace std;
typedef long long ll;
const int MODULO = 1000000007;
const int INF = 100000000; //1e8

typedef long long ll;
typedef pair<int,int> Pii;
typedef pair<ll,ll> Pll;
typedef complex<double> Cd;

bool ok(int i,string l,string r,string a){
	replace(l.begin(),l.end(),'X',(char)('0'+i));
	replace(r.begin(),r.end(),'X',(char)('0'+i));
	replace(a.begin(),a.end(),'X',(char)('0'+i));
	if(i == 0){
		if(l.length() != 1 && l[l.length() - 1] == '0') return false;
		if(r.length() != 1 && r[r.length() - 1] == '0') return false;
		if(a.length() != 1 && a[a.length() - 1] == '0') return false;
	}
	string out;
	bool up = false;
	for (int i = 0; i < (int)max(l.length(),r.length()); i++){
		int add = up;
		add += ((int)l.length() > i) ? (l[l.length() - i - 1] - '0') : 0;
		add += ((int)r.length() > i) ? (r[r.length() - i - 1] - '0') : 0;
		if(add >= 10){
			add -= 10;
			up = true;
		} else {
			up = false;
		}
		out.insert(out.begin(),((char)add + '0'));
	}
	if(up)
		out.insert(out.begin(),'1');

	return out == a;
}

bool solve()
{
	string s;
	if(!(cin>>s)) return false;
	replace(s.begin(),s.end(),'+',' ');
	replace(s.begin(),s.end(),'=',' ');
	istringstream iss(s);
	string l,r,a; iss>>l>>r>>a;
	for (int i = 0; i <= 9; i++){
		if(ok(i,l,r,a)){
			printf("%d\n",i);
			return true;
		}
	}
	puts("NA");
	return true;
}

int main(){
	while(true){
		if(!solve()) break;
	}

	return 0;
}