#include <bits/stdc++.h>

using namespace std;


string Formulation, StrNum1, StrNum2, StrSum, StrTmp;

void solve() {
	int index, len1, len2, maxLength, num1, num2, sum, a;
	string tmp;
	size_t pos;

	len1 = StrNum1.size();
	len2 = StrNum2.size();
	maxLength = max(len1, len2);
	for (int x = 0; x < 10; x++) {
		pos = StrSum.find('X',0);
		while ( pos != string::npos) {
			//cout << pos << endl;
			StrSum[pos] = x + '0';
			pos = StrSum.find('X', pos);
		}
		tmp = "";
		a = 0;
		for (index = 0; index < maxLength; index++) {
			if (index < len1 && index < len2) {
				num1 = (StrNum1[len1 - 1 - index] == 'X' ? x : StrNum1[len1 - 1 - index] - '0');
				num2 = (StrNum2[len2 - 1 - index] == 'X' ? x : StrNum2[len2 - 1 - index] - '0');
				sum = num1 + num2 + a;
			}
			else if (index < len1) {
				num1 = (StrNum1[len1 - 1 - index] == 'X' ? x : StrNum1[len1 - 1 - index] - '0');
				sum = num1 + a;
			}
			else if (index < len2) {
				num2 = (StrNum2[len2 - 1 - index] == 'X' ? x : StrNum2[len2 - 1 - index] - '0');
				sum = num2 + a;
			}

			a = 0;
			if (sum > 9) {
				a = 1;
				sum %= 10;
			}
			tmp += sum + '0';
		}
		if (a == 1) {
			tmp += '1';
		}
		reverse(tmp.begin(), tmp.end());
		//cout << "X=" << x << endl << "StrSum=" << StrSum << endl << "StrTmp=" << tmp << endl;
		if (tmp == StrSum) {
			cout << x << endl;
			return;
		}
		StrSum = StrTmp;
	}
	cout << "NA" << endl;
	return;
}

int main() {
	int i;

	while ( cin >> Formulation ) {
		//cout << Formulation << endl;
		StrNum1 = StrNum2 = StrSum = "";
		i = 0;
		while (Formulation[i] != '+') {
			StrNum1 += Formulation[i];
			i++;
		}
		i++;
		while (Formulation[i] != '=') {
			StrNum2 += Formulation[i];
			i++;
		}
		i++;
		while (Formulation[i] != '\0') {
			StrSum += Formulation[i];
			i++;
		}
		StrTmp = StrSum;
		solve();
		StrTmp = "";
	}

	return 0;
}
