#include <iostream>
#include <iomanip>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <functional>

using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int,int> PII;
typedef long long ll;
typedef unsigned long long ull;

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); i++ )
#define UREP( i, m, n ) for ( unsigned int i = (unsigned int)( m ); i < (unsigned int)( n ); i++ )

#define ITER( c ) __typeof( (c).begin() )
#define IREP( c, it ) for ( ITER(c) it = c.begin(); it != c.end(); ++it )
#define ALL( c ) (c).begin(), (c).end()
#define RALL( c ) (c).rbegin(), (c).rend()

#define PB( n ) push_back( n )
#define MP( a, b ) make_pair( ( a ), ( b ) )
#define EXIST( c, e ) ( (c).find( e ) != (c).end() )

#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl
#define DEBUG( x ) cerr << __FILE__ << ":" << __LINE__ << ": " << #x << " = " << ( x ) << endl

void solve( string org )
{
	for ( char x = '0'; x <= '9'; x++ )
	{
		string str = org;

		bool isTop = true;

		UREP( i, 0, str.length() )
		{
			switch ( str[i] )
			{
			case '+':
			case '=':
				str[i] = ' ';
				isTop = true;
				break;
			case 'X':
				if ( isTop && x == '0' )
				{
					continue;
				}

				isTop = false;
				str[i] = x;
				break;
			default:
				isTop = false;
				break;
			}
		}
		
		int a, b, c;
		istringstream( str ) >> a >> b >> c;

		if ( a + b == c )
		{
			cout << x << endl;
			return;
		}
	}

	cout << "NA" << endl;
	return;
}

int main()
{
	string str;

	while ( cin >> str )
	{
		solve( str );
	}

	return 0;
}