#include <iostream>
#include <string>

using namespace std;

string reverse(string a) {
	if (a.size() == 1) {
		return a;
	} else {
		return reverse(a.substr(1))+a[0];
	}
}

int main() {
	string s;
	while (cin >> s) {
		string a, b, c;
		int r = 0;
		for (int i = 0; i < s.size(); i++) {
			if (s[i] == '+') {
				r++;
			} else if (s[i] == '=') {
				r++;
			} else {
				if (r == 0) {
					a += s[i];
				} else if (r == 1) {
					b += s[i];
				} else {
					c += s[i];
				}
			}
		}
		//cout << a << ' ' << b <<  ' ' << c << endl;
		bool h = false;
		if (a[0] == 'X' || b[0] == 'X' || c[0] == 'X') {
			h = true;
		}
		a = reverse(a);
		b = reverse(b);
		c = reverse(c);
		int d = -1;
		for (int i = 0; i < 10; i++) {
			//cout << i << endl;
			if (a.size() > c.size() || b.size() > c.size()) {
				break;
			}
			if (i == 0 && h) {
				continue;
			}
			int p = 0;
			bool hh = true;
			for (int j = 0; j < c.size(); j++) {
				//cout << i << ' ' << j << endl;
				int aa, bb, cc;
				aa = bb = cc = 0;
				if (j < a.size()) {
					if (a[j] == 'X') {
						aa = i;
					} else {
						aa = a[j]-'0';
					}
				}
				if (j < b.size()) {
					if (b[j] == 'X') {
						bb = i;
					} else {
						bb = b[j]-'0';
					}
				}
				if (c[j] == 'X') {
					cc = i;
				} else {
					cc = c[j]-'0';
				}
				if ((aa+bb+p)%10 == cc) {
					if (aa+bb+p > 9) {
						p = 1;
					} else {
						p = 0;
					}
				} else {
					hh = false;
					break;
				}
			}
			if (hh) {
				d = i;
				break;
			}
		}
		if (d == -1) {
			cout << "NA" << endl;
		} else {
			cout << d << endl;
		}
	}
	return 0;
}