#include<bits/stdc++.h>
using namespace std;
int main(){
  int m,f,b;
  cin >> m >> f >> b;
  if(m<b&&b<=m+f)
    cout << b-m << endl;;
  if(m+f<b)
    cout << "NA" << endl;
  if(m>=b)
    cout << 0 << endl;
  return 0;
}