#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using pii = pair<int, int>;

int main() {
  ll b, c;
  cin >> b >> c;

  ll ans = 0;
  if (b > 0) {
    ll l1 = b - c / 2;
    ll r1 = b + (c - 2) / 2;
    ll l2 = -b - (c - 1) / 2;
    ll r2 = -b + (c - 1) / 2;

    ans += r1 - l1 + 1;
    ans += r2 - l2 + 1;

    if (l1 <= r2) ans -= r2 - l1 + 1;
  }
  else {
    ll l1 = b - c / 2;
    ll r1 = b + (c - 2) / 2;
    ll l2 = -b - (c - 1) / 2;
    ll r2 = -b + (c - 1) / 2;

    ans += r1 - l1 + 1;
    ans += r2 - l2 + 1;
    
    if (l2 <= r1) ans -= r1 - l2 + 1;
  }

  cout << ans << endl;
  return 0;
}
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
#define rep(i,n) for(int i=0;i<int(n);i++)
#define rep1(i,n) for(int i=1;i<=int(n);i++)
#define per(i,n) for(int i=int(n)-1;i>=0;i--)
#define per1(i,n) for(int i=int(n);i>0;i--)
#define all(c) c.begin(),c.end()
#define si(x) int(x.size())
#define pb emplace_back
#define fs first
#define sc second
template<class T> using V = vector<T>;
template<class T> using VV = vector<vector<T>>;
template<class T,class U> void chmax(T& x, U y){if(x<y) x=y;}
template<class T,class U> void chmin(T& x, U y){if(y<x) x=y;}
template<class T> void mkuni(V<T>& v){sort(all(v));v.erase(unique(all(v)),v.end());}
template<class T> int lwb(const V<T>& v, const T& a){return lower_bound(all(v),a) - v.begin();}
template<class S,class T> ostream& operator<<(ostream& o,const pair<S,T> &p){
	return o<<"("<<p.fs<<","<<p.sc<<")";
}
template<class T> ostream& operator<<(ostream& o,const vector<T> &vc){
	o<<"{";
	for(const T& v:vc) o<<v<<",";
	o<<"}";
	return o;
}
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }

#ifdef LOCAL
#define show(x) cerr << "LINE" << __LINE__ << " : " << #x << " = " << (x) << endl
void dmpr(ostream& os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ~ ";
	dmpr(os,args...);
}
#define shows(...) cerr << "LINE" << __LINE__ << " : ";dmpr(cerr,##__VA_ARGS__)
#define dump(x) cerr << "LINE" << __LINE__ << " : " << #x << " = {";  \
	for(auto v: x) cerr << v << ","; cerr << "}" << endl;
#else
#define show(x) void(0)
#define dump(x) void(0)
#define shows(...) void(0)
#endif

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);		//DON'T USE scanf/printf/puts !!
	cout << fixed << setprecision(20);

	ll x,c; cin >> x >> c;
	ll p = x-c/2, q = max(x,x+c/2-1);
	ll r = (-x-(c-1)/2), s = (-x+(c-1)/2);
	cout << (q-p+1) + (s-r+1) - max(min(q,s)-max(p,r)+1,0LL) << endl;
}
