#include <iostream>
#include <cstdio>
#include <string>
using namespace std;
#define rep(x,to) for(int x = 0; x < (to); ++(x))
int main() {
	string s;
	while(cin >> s) {
		int a[128], b[128], c[128], la, lb, lc;
		rep(j,128) {
			a[j] = b[j] = c[j] = 0;
		}
		int i = 0;
		for(; s[i] != '+'; i++) {
			if(s[i] == 'X') a[i] = -1;
			else a[i] = s[i] - '0';
		}
		la = i;
		i++;

		for(; s[i] != '='; i++) {
			if(s[i] == 'X') b[i-la-1] = -1;
			else b[i-la-1] = s[i] - '0';
		}
		lb = i - la - 1;
		i++;

		for(; s[i] != '\0'; i++) {
			if(s[i] == 'X') c[i-la-lb-2] = -1;
			else c[i-la-lb-2] = s[i] - '0';
		}
		lc = i - la - lb - 2;
		
		if(la > lc || lb > lc) {
			cout << "NA" << endl;
			continue;
		}
		rep(j,lc) {
			if(j<la)a[lc-1-j] = a[la-1-j];
			else a[lc-1-j] = 0;
		}
		rep(j,lc) {
			if(j<lb)b[lc-1-j] = b[lb-1-j];
			else b[lc-1-j] = 0;
		}
		
		bool ret = 1;
		rep(i,10) {

			int na[128], nb[128], nc[128];
			if(i == 0 && lc > 1 && (a[lc-la] == -1 || b[lc-lb] == -1 || c[0] == -1)) continue;
			
			rep(j,lc) {
				if(a[j] == -1) na[j] = i;
				else na[j] = a[j];
				if(b[j] == -1) nb[j] = i;
				else nb[j] = b[j];
				if(c[j] == -1) nc[j] = i;
				else nc[j] = c[j];
			}
			
			bool f = 0;
			ret = 1;
			for(int j = lc-1; j >= 0; j--) {
				int x = na[j] + nb[j] + f;
				f = 0;
				if(x >= 10) f = 1, x -= 10;
				if(nc[j] != x) {
					ret = 0;
					break;
				}
			}
			if(f) ret = 0;
			if(ret) {
				cout << i << endl;
				break;
			}
		}
		if(!ret) cout << "NA" << endl;
	}
	return 0;
}