#include <cstdio>
#include <vector>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <sstream>
#include <cmath>
#include <climits>
#include <set>
#include <iostream>
#include <map>
#include <functional>
#include <cstdlib>
#include <numeric>
#include <queue>
#include <complex>
#include <sstream>
#include <stack>

using namespace std;

#define reep(i,f,n) for(int i=f; i<int(n); ++i)
#define rep(i,n) reep(i,0,n)

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef complex<double> Point;

int main()
{
	char exp[128];
	while(scanf("%s", exp) != EOF){
		int N = strlen(exp);
		char num[4][64];
		int index = 0;
		int count = 0;
		rep(j, N+1){
			if(j==N || !isalnum(exp[j])){
				strncpy(num[count], exp+index, j-index);
				num[count][j-index] = '\0';
				index = j+1;
				++count;
			}
		}
		
		int ans = -1;
		rep(i, 10){
			bool ok = true;
			char a[4][64];
			rep(j, 3){
				strcpy(a[j], num[j]);
				rep(k, strlen(a[j])){
					if(a[j][k] == 'X'){
						if(k == 0 && i == 0 && strlen(a[j]) > 2){
							j = 3;
							ok = false;
							break;
						}
						a[j][k] = i + '0';
					}
				}
			}
			if(!ok)
				continue;
			if(atoi(a[0])+atoi(a[1])==atoi(a[2])){
				ans = i;
				break;
			}
		}
		if(ans == -1)
			puts("NA");
		else
			printf("%d\n", ans);
	}

	return 0;
}