#include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<algorithm>
#include<map>
using namespace std;

int parse(string a) {
	int s = 0;
	for (char b : a) {
		s *= 10;
		s += b - 48;
	}
	return s;
}
vector<string>split(string a) {
	vector<string>b;
	string c = "";
	for (char d : a) {
		if (d == '=' || d == '+') {
			b.push_back(c);
			c = "";
		}
		else c += d;
	}
	b.push_back(c);
	return b;
}
int main() {
	string a;
	while (cin >> a) {
		for (int c = 0; c < 10; c++) {
			string b = a;
			for (int d = 0; d < b.length(); d++) {
				if (b[d] == 'X')b[d] = c + 48;
			}
			vector<string>e = split(b);
			if (!(e[0].length() != 1 && e[0][0] == '0') && !(e[1].length() != 1 && e[1][0] == '0') && !(e[2].length() != 1 && e[2][0] == '0')) {
				if (parse(e[0]) + parse(e[1]) == parse(e[2])) { cout << c << endl; break; }
			}
			if (c == 9)cout << "NA" << endl;
		}
	}
}