#include<iostream>
#include<sstream>
#include<algorithm>
#include<climits>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<ctime>
#include<cfloat>
#include<functional>
#include<map>
#include<string>
#include<cstring>
#include<vector>
#include<queue>
#include<stack>
#include<deque>
#include<set>
#include<bitset>
#include<list>
#include<numeric>
#include<complex>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<long long, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<long long, long long> ll_ll;
typedef pair<double, double> d_d;

#define PI 3.141592653589793238462643383279
#define mod 1000000007LL
#define rep(i, n) for(i = 0;i < n;++i)
#define rep1(i, n) for(i = 1;i < n;++i)
#define rep2d(i, j, n) for(i = 0;i < n;++i)for(j = i + 1;j < n;++j)
#define per(i, n) for(i = n - 1;i > -1;--i)
#define int(x) int x; scanf("%d",&x)
#define int2(x, y) int x, y; scanf("%d%d",&x, &y)
#define int3(x, y, z) int x, y, z; scanf("%d%d%d",&x, &y, &z)
#define scn(n, a) rep(i, n)cin >> a[i]
#define sc2n(n, a, b) rep(i, n)cin >> a[i] >> b[i]
#define pri(x) cout << x << "\n"
#define pri2(x, y) cout << x << " " << y << "\n"
#define pri3(x, y, z) cout << x << " " << y << " " << z << "\n"
#define pb push_back
#define mp make_pair
#define all(a) (a).begin(),(a).end()
#define endl "\n"
#define kabe puts("---------------------------")
#define kara puts("")
#define debug(x) cout << " --- " << x << "\n"
#define debug2(x, y) cout << " --- " << x << " " << y << "\n"
#define debug3(x, y, z) cout << " --- " << x << " " << y << " " << z << "\n"
#define X first
#define Y second
#define eps 0.0001
#define prid(x) printf("%.15lf\n", x)
#define N 150


signed main(void){
  int i, j, k;
  for(int testcase = 0;testcase < 1234567;testcase++){
    string s;
    for(;getline(cin, s);){
      int lh[N] = {0}, rh[N] = {0};
      int lhx[N] = {0}, rhx[N] = {0};
      for(i = s.size() - 1;;--i){
        if(s[i] == '=')break;
        else if(s[i] == 'X')rhx[s.size() - 1 - i]++;
        else rh[s.size() - 1 - i] += (int)(s[i] - '0');
      }
      --i;
      for(j = i;;--j){
        if(s[j] == '+')break;
        else if(s[j] == 'X')lhx[i - j]++;
        else lh[i - j] += (int)(s[j] - '0');
      }
      i = j - 1;
      for(j = i;j >= 0;--j){
        if(s[j] == 'X')lhx[i - j]++;
        else lh[i - j] += (int)(s[j] - '0');
      }
/*
      rep(i, 10){
        debug(i);
        printf("lh : %d + %dx\n", lh[i], lhx[i]);
        printf("rh : %d + %dx\n", rh[i], rhx[i]);
      }
*/

      rep(k, 10){
        int l = 0, r = 0;
        rep(i, N){
          if((lh[i] + lhx[i] * k + l) % 10 != (rh[i] + rhx[i] * k + r) % 10)break;
          l = (lh[i] + lhx[i] * k + l) / 10;
          r = (rh[i] + rhx[i] * k + r) / 10;
        }
        if(i == N){
          pri(k); break;
        }
      }
      if(k == 10)pri("NA");
      s.clear();
    }

/*/

//*/ break;
  }
  return 0;
}