#include<iostream>
using namespace std;

int main()
{
    int m, f, b;

    cin >> m >> f >> b;

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

    return 0;
}
