#include <iostream>
using namespace std;
int main()
{ int a,b,a1,b1,k=0,nrc1=0,nrc2=0;
cin>>a>>b;//citim a si b
a1=a;
b1=b;//copiem a si b in 2 variabile
while(a1)
{
if(a1>0)
nrc1++;
a1=a1/10; // aflam cate cifre are a
}
while(b1)
{
if(b1>0)
nrc2++;
b1=b1/10;//aflam cate cifre are b
}
if(nrc1!=nrc2)//verificam daca au acelasi nr de cifre
cout<<"NU";
else
{
while(a && b)
{ if(a%10==b%10)//aflam cate cifre identice se afla pe aceleasi pozitii
k++;
a=a/10;
b=b/10;
}
cout<<k;
}
}