#include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <climits>
#include <cfloat>
using namespace std;

int main()
{
    for(;;){
        string s0;
        if(!(cin >> s0))
            return 0;

        int a = s0.find('+');
        int b = s0.find('=');
        vector<string> s(3);
        s[0] = s0.substr(0, a);
        s[1] = s0.substr(a+1, b-a-1);
        s[2] = s0.substr(b+1);

        bool notZero = false;
        int n = 0;
        for(int i=0; i<3; ++i){
            if(s[i][0] == 'X' && s[i] != "X")
                notZero = true;
            n = max(n, (int)s[i].size() + 1);
        }
        for(int i=0; i<3; ++i)
            s[i] = string(n-s[i].size(), '0') + s[i];

        bool na = true;
        for(int i=0; i<=9; ++i){
            if(i == 0 && notZero)
                continue;

            vector<string> s1 = s;
            for(int j=0; j<3; ++j)
                replace(s1[j].begin(), s1[j].end(), 'X', (char)(i+'0'));

            bool ok = true;
            int c = 0;
            for(int j=n-1; j>=0; --j){
                int sum = s1[0][j] - '0' + s1[1][j] - '0' + c;
                c = sum / 10;
                sum %= 10;
                if(sum != s1[2][j] - '0'){
                    ok = false;
                    break;
                }
            }

            if(ok){
                na = false;
                cout << i << endl;
                break;
            }
        }

        if(na)
            cout << "NA" << endl;
    }
}