#include <iostream>
#include <string.h>
#include <stdio.h>
using namespace std;
int main(void){
    int m,f,b;
    cin>>m>>f>>b;
    if(m+f<b)cout<<"NA"<<endl;
    else{
        if(m>=b)cout<<0<<endl;
        else cout<<b-m<<endl;
    }
}

