#include<iostream>
#include<string>

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;
}

