#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define all(a)  (a).begin(),(a).end()
#define pb push_back
#define INF 999999999
#define int ll

vector<string> split(string s,char ch){
    vector<string> ret;
    string tmp ="";
    rep(i,s.size()){
        if(s[i]==ch){
            ret.pb(tmp);
            tmp = "";
        }else tmp+=s[i];
    }
    if(tmp.size())ret.pb(tmp);
    return ret;
}

string addString(string a,string b ){
    if(a.size()<b.size())swap(a,b);         //len(a)>len(b)???
    b = string(a.size()-b.size(),'0')+b;    //b????????????a??¨??????????????????????????????0??§?????????
    
    string ans = string(a.size()+1,'0');    //a?????????+1 ?????????0??§???????????????
    for(int i=(int)a.size()-1;i>=0;i--){    //?¶??????? & ??°????????????
        ans[i+1] += (a[i]-'0') + (b[i]-'0');
        if(ans[i+1]>='0'+10){
            ans[i] += 1;
            ans[i+1] -= 10;
        }
    }
    string ret = "";                        //??????????????°???0????¶????
    rep(i,ans.size()){
        if(ans[i]!='0'||i==ans.size()-1){
            ret = ans.substr(i,ans.size()-i);
            break;
        }
    }
    return ret;
}


bool is(string s){
    rep(i,s.size())if(s[i]=='+')s[i]='=';
    vector<string> res = split(s,'=');
    rep(i,res.size()){
        if(res[i].size()>=2&&res[i][0]=='0')return false;
    }
    if(addString(res[0],res[1])==res[2])return true;
    return false;
}



signed main(){
    string s;
    while(cin>>s){
        rep(i,10){
            string tmp = s;
            rep(j,tmp.size())if(tmp[j]=='X')tmp[j]='0'+i;
            if(is(tmp)){
                cout<<i<<endl;
                break;
            }
            if(i==9)cout<<"NA"<<endl;
        }
    }
}