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

string getNumber( string& formula, int* index, int n )
{
	string ret;
	while( ( formula[ *index ] >= '0' && formula[ *index ] <= '9' ) || formula[ *index ] == 'X' ){
		if( formula[ *index ] == 'X' ){
			ret += ( n + '0' );
		}else{
			ret += formula[ *index ];
		}
		++*index;
	}
	return ret;
}

void advance( string& formula, int* index ){
	while( !( ( formula[ *index ] >= '0' && formula[ *index ] <= '9' ) || formula[ *index ] == 'X') ){
		++*index;
	}
}

bool compare( string& left, string& right, string& answer )
{
	string sum;
	int carry = 0;
	for( int l = left.size() - 1, r = right.size() - 1; l >= 0 || r >= 0; --l, --r ){
		char lc = '0';
		char rc = '0';
		if( l >= 0 ){
			lc = left[ l ];
		}
		if( r >= 0 ){
			rc = right[ r ];
		}
		int d = ( lc - '0' + rc - '0' + carry );
		sum = (char)( d % 10 + '0' ) + sum;
		carry = d / 10;
	}
	if( carry ){
		sum = (char)( carry + '0' ) + sum;
	}
	if( sum == answer ){
		return true;
	}
	return false;
}

int main()
{
	string formula;

	while( cin >> formula ){
		bool find = false;
		for( int i = 0; i < 10; ++i ){
			int index = 0;
			string left = getNumber( formula, &index, i );
			advance( formula, &index );
			string right = getNumber( formula, &index, i );
			advance( formula, &index );
			string answer = getNumber( formula, &index, i );
			if( ( left.size() > 1 && left[ 0 ] == '0' ) 
				|| ( right.size() > 1 && right[ 0 ] == '0' )
				|| ( left.size() > 1 &&  answer[ 0 ] == '0' ) ){
				continue;
			}
			if( compare( left, right, answer ) ){
				cout << i << endl;
				find = true;
				break;
			}
		}
		if( !find ){
			cout << "NA" << endl;
		}
	}
	return 0;
}