#include<iostream>
#include<algorithm>
#include<vector>
#include<stack>
#include<map>
#include<set>
#include<queue>
#include<cstdio>
#include<climits>
#include<cmath>
#include<cstring>
#include<string>
#include<sstream>

#define f first
#define s second
#define mp make_pair

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,c) for(__typeof((c).begin()) i=(c).begin(); i!=(c).end(); i++)
#define ALL(c) (c).begin(), (c).end()

using namespace std;

typedef unsigned int uint;
typedef long long ll;

class BigInteger{
private:
  void fromStr(const std::string &str){
    int len = str.size();
    int tmp = 0;

    if(str[0] == '+'){
      sign = 1;
      tmp=1;
    }else if (str[0] == '-'){
      sign = -1;
      tmp=1;
    }else{
      sign = 1;
    }

    nums = std::vector<char>(len-tmp);
    for(int i=0;i<len-tmp;i++){
      nums[i]=str[len-1-i]-'0';
    }
  }
public:
  std::vector<char> nums;
  char sign;
  /*
   * constructors
   */
  BigInteger(){sign = 1;nums = std::vector<char>(1,0);}
  BigInteger(const std::vector<char> n,char s){
    nums = n;
    sign = s;
  }
  BigInteger(const std::string &str){
    fromStr(str);
  }
  BigInteger(int n){
    char buff[16];
    sprintf(buff,"%d",n);
    fromStr(std::string(buff));
  }

  int size() const{
    return nums.size();
  }
  int len() const{
    return nums.size();
  }

  char operator [] (int n) const{
    if(n<size() && n>=0)
      return nums[n];
    else
      return 0;
  }

  const std::vector<char> &vec() const{
    return nums;
  }
  char sig() const{
    return sign;
  }

  std::string toString() const{
    std::string ret="";
    if(sign == -1) ret+="-";
    for(int i=nums.size()-1;i>=0;i--){
      ret+=nums[i]+'0';
    }
    return ret;
  }

  void debug() const{
    std::cout << "sign =" << (int)sign << std::endl;
    for(int i=nums.size()-1;i>=0;i--){
      std::cout << (int)nums[i] << " ";
    }
    std::cout << std::endl;
  }
};

bool operator == (const BigInteger &a,const BigInteger &b){
  char as = a.sig();
  char bs = b.sig();
  if(as != bs) return false;

  if(a.len() != b.len()){
    return false;
  }else{
    for(int i=0;i<a.len();i++){
      if(a[i]!=b[i]) return false;
    }
  }
  return true;
}

BigInteger operator + (const BigInteger &a,const BigInteger &b){
  int lena = a.size();
  int lenb = b.size();
  int maxlen = std::max(lena,lenb);
  std::vector<char> v = std::vector<char>(maxlen+1,0);
  int sig = 1;

  for(int i=0;i<maxlen;i++){
    v[i] += a.sig()*a[i]+b.sig()*b[i];
    while(v[i] < 0){
      v[i+1]--;
      v[i]+=10;
      std::cout << "test" << std::endl;
    }
    if(v[i] >=10){
      v[i+1] = v[i]/10;
      v[i]%=10;
    }
  }

  if(v[maxlen]<0){
    sig = -1;
    for(int i=0;i<maxlen;i++){
      v[i]=-v[i];
      while(v[i]<0){
        v[i+1]++;
        v[i]+=10;
      }
    }
    v[maxlen]=-v[maxlen];
  }

  int pos=v.size();
  while(pos!=1 && v[pos-1]==0) pos--;
  if(pos != v.size()) v.resize(pos);

  return BigInteger(v,sig);
}

int main(){
  string str;
  while(cin>>str){
    int posP, posE;
    posP = str.find('+');
    posE = str.find('=');

    string op1, op2, ans;
    op1 = str.substr(0, posP);
    op2 = str.substr(posP+1, posE - posP - 1);
    ans = str.substr(posE+1);
    //cout << op1 << " + " << op2 << " = " << ans << endl;

    bool canZero = true;
    if((op1.size() != 1 && op1[0] == 'X') ||
       (op2.size() != 1 && op2[0] == 'X') ||
       (ans.size() != 1 && ans[0] == 'X'))
      canZero = false;

    int ret = -1;
    for(char c = (canZero ? '0' : '1'); c <= '9'; c++){
      string opt1=op1, opt2=op2, anst=ans;
      while(opt1.find('X') != -1) opt1[opt1.find('X')] = c;
      while(opt2.find('X') != -1) opt2[opt2.find('X')] = c;
      while(anst.find('X') != -1) anst[anst.find('X')] = c;
      BigInteger a(opt1);
      BigInteger b(opt2);
      BigInteger d(anst);

      if(a+b == d){
        ret = c - '0';
        break;
      }
    }
    if(ret == -1) cout << "NA" << endl;
    else cout << ret << endl;
  }
  return 0;
}