#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
#define R(s) reverse(s,s+strlen(s))
#define C(s) (!s[1]||s[0]-'0')
void F(char*p,char c)
{
	for(;p=strchr(p,'X');++p)
		*p=c;
}
int main()
{
	char s[128];
	while(scanf("%s",s)>0)
	{
		char a[128]="",b[128]="",c[128]="",i,n;
		for(n=0;n<=9;++n)
		{
			sscanf(s,"%[^+]+%[^=]=%s",a,b,c);
			F(a,n+'0');
			F(b,n+'0');
			F(c,n+'0');
			if(C(a)&&C(b)&&C(c))
			{
				R(a);
				R(b);
				R(c);
				int f=1,g=1;
				char d[128]="";
				for(i=0;;++i)
				{
					if(f)f=a[i];
					if(g)g=b[i];
					if(!f&&!g)break;
					if(d[i])d[i]-='0';
					if(f)d[i]+=a[i]-'0';
					if(g)d[i]+=b[i]-'0';
					if(d[i]>9)d[i+1]+='0'+d[i]/10, d[i]%=10;
					d[i]+='0';
				}
				if(!strcmp(c,d))goto N;
			}
		}
		puts("NA");continue;
N:;printf("%d\n",n);
	}
	return 0;
}