#include<iostream>
#include<cstdio>
#include<string>
using namespace std;
typedef long long Int;

int val(char c, int x){
	if(c == 'X')return x;
	return c - '0';
}

string add(string a, string b, int x){
	string res = "";
	int up = 0;
	if(a.size() > b.size())swap(a,b);
	for(int i = 0;i < b.size();i++){
		int num = val(b[b.size() - 1 - i], x);
		if((int)a.size() - 1 - i >= 0){
			num += val(a[a.size() - 1 - i], x);
		}
		num += up;
		res = (char)((num%10) + '0') + res;
		up =  num / 10;
	}
	if(up)res = '1' + res;
	return res;
}

string replace(string s, int x){
	string res = "";
	for(int i = 0;i < s.size();i++){
		if(s[i] == 'X')res += char('0' + x);
		else res += s[i];
	}
	return res;
}

void solve(string a, string b, string c){
	for(int i = 0;i <= 9;i++){
		if(a.size() != 1 && a[0] == 'X' || b.size() != 1 && b[0] == 'X' || c.size() != 1 && c[0] == 'X')if(i == 0)continue;
		if(replace(c, i) == add(a, b, i)){
			cout << i << endl;
			return;
		}
	}
	cout << "NA" << endl;
}

int main(){
	string str, a[3];
	char s[129];
	while(~scanf(" %s\n", s)){
		str = s;
		a[0] = a[1] = a[2] = "";
		int x = 0;
		if(str == "")return 0;
		for(int i = 0;i < str.size();i++){
			if(str[i] == '+' || str[i] == '=')x++;
			else a[x] += str[i];
		}
		
		solve(a[0], a[1], a[2]);
	}
	return 0;
}