#include <bits/stdc++.h>
using namespace std;
int main(void){
    long long n,b;
    cin>>n>>b;
    if(n%2==1){
        cout<<((n-1)/2)%b<<endl;
    }else if(b%2==0){
        cout<<"NaN"<<endl;
    }else{
        cout<<((n-1)+b)/2<<endl;
    }
    return 0;
}