#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<string>

using namespace std;

void AlphameticReplace(string &s, int r, char X){
	for(unsigned int i = 0; i < s.length(); i++){
		//if( i == 0 && r == 0 ) return ;
		if( s[i] == X ) s[i] = r + '0';
	}
}
string AddBigInteger(string s1, string s2){
	string ret;
	if(s2.length() > s1.length()) return AddBigInteger(s2, s1);
	else{
		int overflow = 0;
		reverse(s1.begin(), s1.end());
		reverse(s2.begin(), s2.end());
		for(unsigned int i = 0; i < s1.length(); i++){
			int d =(s1[i] - '0')+ ( i >= s2.length() ? 0 : (s2[i] - '0') )+overflow;
			if( d >= 10 ){overflow = 1;d -= 10;}else overflow = 0;
			ret += d + '0';
		}
		if( overflow > 0 ) ret += '1';
	}
	reverse(ret.begin(), ret.end());
	return ret;
}

int main(void){
	while( true ){
		int ans;
		bool bFound = false;
		string s,a,b,c;

		cin >> s;
		if( cin.eof() ) break;

		a = s.substr(0, s.find('+'));
		b = s.substr(s.find('+')+1, s.find('=') - (s.find('+')+1));
		c = s.substr(s.find('=')+1);

		for(int x = 0; x < 10; x++){
			string ta = a, tb = b, tc = c;
			AlphameticReplace(ta, x, 'X');
			AlphameticReplace(tb, x, 'X');
			AlphameticReplace(tc, x, 'X');
			if( tc.compare(AddBigInteger(ta, tb)) == 0 ){
				ans = x;
				bFound = true;
			}
		}
		if( bFound ){
			cout << ans << '\n';
		}else{
			cout << "NA\n";
		}
	}
	return 0;
}