#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 len[4];
		
		{
			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';
					len[count] = strlen(num[count]);
					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, len[j]){
					if(a[j][k] == 'X'){
						if(k == 0 && i == 0 && len[j] > 1){
							ok = false;
							break;
						}
						a[j][k] = i + '0';
					}
				}
				if(!ok)
					break;
				reverse(a[j], a[j]+len[j]);
			}
			if(!ok)
				continue;

			int rise = 0;
			for(int j=0; j<max(len[0], len[1]) || rise; ++j){
				int next = (j<len[0] ? a[0][j]-'0' : 0) + (j<len[1] ? a[1][j]-'0' : 0) + rise;
				if(len[2]<=j || a[2][j]-'0' != next%10){
					ok = false;
					break;
				}
				rise = next / 10;
			}
			if(ok){
				ans = i;
				break;
			}
		}
		if(ans == -1)
			puts("NA");
		else
			printf("%d\n", ans);
	}

	return 0;
}