#include <iostream>
#include <cstdio>

using namespace std;

int main(){
	
	string str, str_a, str_b, str_c;
	
	while(true){
		
		cin >> str;
		
		if(cin.eof()){
			break;
		}
		
		for(int i = 0; i < str.size(); i++){
			if(str[i] == '+'){
				str_a = str.substr(0, i);
			}
			if(str[i] == '='){
				str_b = str.substr(str_a.size() + 1, i - 1 - str_a.size());
				str_c = str.substr(i + 1);
			}
		}
		
		string str_a2, str_b2, str_c2, str_ab;
		
		for(int i = 0; i <= 9; i++){
			str_a2 = str_a;
			str_b2 = str_b;
			str_c2 = str_c;
			str_ab = str_c;
			for(int j = 0; j < str_a2.size(); j++){
				if(str_a2[j] == 'X'){
					str_a2[j] = '0' + i;
				}
			}
			for(int j = str_a2.size(); j < str_ab.size(); j++){
				str_a2 = "0" + str_a2;
			}
			for(int j = 0; j < str_b2.size(); j++){
				if(str_b2[j] == 'X'){
					str_b2[j] = '0' + i;
				}
			}
			for(int j = str_b2.size(); j < str_ab.size(); j++){
				str_b2 = "0" + str_b2;
			}
			for(int j = 0; j < str_c2.size(); j++){
				if(str_c2[j] == 'X'){
					str_c2[j] = '0' + i;
				}
			}
			for(int j = 0; j < str_ab.size(); j++){
				str_ab[j] = '0';
			}
			
			for(int j = str_ab.size() - 1; j >= 0; j--){
				str_ab[j] = str_ab[j] + str_a2[j] + str_b2[j] - '0' - '0';
				if(str_ab[j] > '9'){
					str_ab[j] -= 10;
					if(j >= 1){
						str_ab[j - 1] += 1;
					}else{
						str_ab = "1" + str_ab;
					}
				}
			}
			//cout << str_c2 << endl << str_ab << endl << endl;
			if(str_c2 == str_ab){
				printf("%d\n", i);
				break;
			}else if(i == 9){
				printf("NA\n");
			}
		}
	}
	
	return 0;
}