// 2017/09/21 Tazoe

#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;
	}

	return 0;
}