#include<iostream>
#include<vector>
using namespace std;

class BigInt{
public:
  vector<int> value;
  int sign;

  void set(int n){
    value.clear();
    if(n==0){
      sign = 0;
      value.push_back(0);
    }else if(n<0){
      sign = -1;
      n *= -1;
    }else{
      sign = 1;
    }
    while(n){
      value.push_back(n%10);
      n/=10;
    }
  }

  void set(string str){
    value.clear();
    if(str[0]=='-')sign = -1;
    else if(str[0]=='0')sign = 0;
    else sign = 1;
    int a = 0;
    if(sign<0)a = 1; 
    for(int i=str.size()-1;i>=a;i--){
      value.push_back(str[i]-'0');
    }
  }

  void print(void){
    if(sign<0)cout << '-';
    for(int i=value.size()-1;i>=0;i--)cout << value[i];
    cout << endl;
  }

  BigInt add(BigInt x){
    int max,min;
    BigInt ans;

    if(sign == 0)return x;
    if(x.sign == 0)return *this;
       
    ans.sign = 1;
    ans.value.clear();
    if(value.size()>x.value.size()){
      max = value.size();
      min = x.value.size();
      for(int i=0;i<min;i++)ans.value.push_back(value[i]+x.value[i]);
      for(int i=min;i<max;i++)ans.value.push_back(value[i]);
    }else{
      max = x.value.size();
      min = value.size();
      for(int i=0;i<min;i++)ans.value.push_back(value[i]+x.value[i]);
      for(int i=min;i<max;i++)ans.value.push_back(x.value[i]);
    }
    for(int i=0;i<(int)ans.value.size()-1;i++){
      while(ans.value[i]>=10){
	ans.value[i]-=10;
	ans.value[i+1]++;
      }
    }
    if(ans.value[ans.value.size()-1]>=10){
      ans.value[ans.value.size()-1]-=10;
      ans.value.push_back(1);
    }
    return ans;
  }

  int cmp(BigInt a){
    if(sign<a.sign)return -1;
    if(sign>a.sign)return 1;
    if(sign == 0)return 0;

    if(value.size()<a.value.size())return -1;
    if(value.size()>a.value.size())return 1;
    for(int i=value.size()-1;i>=0;i--){
      if(value[i]<a.value[i])return -1;
      if(value[i]>a.value[i])return 1;
    }
    return 0;
  }

};

int main(){
  string str,tmp;
  string a,b,c;
  BigInt d,e,f;
  int mode;
  int i,j;

  while(cin >> str){
    for(i=0;i<10;i++){
      tmp = str;
      for(j=0;j<tmp.size();j++){
	if(tmp[j]=='X')tmp[j] = '0' + i;
      }
      a.clear();
      b.clear();
      c.clear();
      mode = 0;
      for(j=0;j<tmp.size();j++){
	if(tmp[j] == '+'){
	  mode++;
	}else if(tmp[j] == '='){
	  mode++;
	}else{
	  if(mode==0)a.push_back(tmp[j]);
	  else if(mode==1)b.push_back(tmp[j]);
	  else c.push_back(tmp[j]);
	}
      }
      d.set(a);
      e.set(b);
      f.set(c);
      if(f.cmp(d.add(e)) == 0){
	cout << i << endl;
	break;
      }
    }
    if(i==10)cout << "NA" << endl;
  }
}