#include<iostream>

using namespace std;

int a,b;

int turn(int x)
{
    int sum=0;
    while(x)
    {
        int t=x%10;
        sum=sum*10+t;
        x/=10;
    }
    return sum;
}

int main()
{
    while(cin>>a>>b)
    {
        int num1=turn(a+b);
        int num2=turn(a)+turn(b);
        if(num1==num2)
        cout<<a+b<<endl;
        else
        puts("NO");
    }
    return 0;
}