#include<bits/stdc++.h>
using namespace std;

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