#include<iostream>;

using namespace std;

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