#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

int main() {
	char sh[150];
	int a,b,c,i,k,f,cal1,cal2,cal3;
	while (cin >> sh) {
		for (i=0;i<10;i++) {
		for (a=0;sh[a]!='+';a++);
		for (b=0;sh[b]!='=';b++);
		c=strlen(sh)-1; a--; b--; k=0; f=0;
		if (i==0) if ((sh[0]=='X' && sh[1]!='+') || (sh[a+2]=='X' && sh[a+3]!='=') || (sh[b+2]=='X' && sh[b+3]!='\0')) continue;
		while(a<200 || b<200) {
			if (a>200) cal1=0; else if (sh[a]=='X') cal1=i; else cal1=sh[a]-'0';
			if (b>200) cal2=0; else if (sh[b]=='X') cal2=i; else cal2=sh[b]-'0';
			if (cal1+cal2+k>=10) {cal1=cal1+cal2+k-10; k=1;} else { cal1=cal1+cal2+k; k=0;}
			if (sh[c]=='X') cal3=i; else cal3=sh[c]-'0';
			if (cal1!=cal3) { f=1; break;}
			a=(a==0) ? 300 : a-1;
			b=(sh[b-1]=='+') ? 300 : b-1;
			c--;
		}
		if ((k==0 && sh[c]!='=') || (k==1 && (sh[c]!='1' || sh[c-1]!='='))) f=1;
		if (f==0) { cout << i << endl; break;}
		}
        if (f==1) cout << "NA" << endl;
	}
	return 0;
}