#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for( int i = 0; i < n; i++ )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000

int i = 0;
string str;

string takeout(char a) {
    if ( i != 0) i++;
    stringstream tmp;
    while (str[i] != a) {
        tmp << str[i];
        i++;
    }
    return tmp.str(); 
}

string change(string str, char a) {
    int j = 0;
    while(str[j] != '\0') {
        if (str[j] == 'X') str[j] = a;
        j++;
    }
    return str;
}

int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    while(cin >> str){
        i = 0;
        string L = takeout('+');
        string R = takeout('=');
        string ANS = takeout('\0');

        int flag = 0;
        for (int i = 0; i < 10; i++){
            string tmp1, tmp2, tmp3;
            tmp1 = change(L, '0' + i);
            tmp2 = change(R, '0' + i);
            tmp3 = change(ANS, '0' + i);
            if (stoll(tmp1) + stoll(tmp2) == stoll(tmp3)) {
                cout << i << endl;
                flag = 1;
                break;
            } 
        }
        if (flag == 0) cout << "NA" << endl;
    }

    return 0;
}