#include <iostream>
using namespace std;
  
int main() {
   int m, f, b;
   cin >> m >> f >> b;

   if ( m >= b ) {
   cout << 0 << endl;
  
   }else if ( m + f >= b ) {
   cout << b - m << endl;
  }
   else 
   cout << "NA" << endl;
}

