#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <set>
#include <queue>
#include <functional>
#include <algorithm>
#include <cmath>

using namespace std;

typedef int64_t ll;

int main(int argc, char *argv[])
{
	ll b, c;
	cin >> b >> c;
	//b = -1e18;
	//c = 1;

	ll pmin = b - (c / 2);
	ll pmax = max(b + (c / 2) - 1, pmin);
	ll pnum = pmax - pmin + 1;//(c / 2) * 2;
	ll nmin = -b - (c - 1) / 2;
	ll nmax = -b + (c - 1) / 2;
	ll nnum = nmax - nmin + 1;//(c - 1) / 2 * 2 + 1;
	ll dnum = 0;

	ll dmin = max(pmin, nmin);
	ll dmax = min(pmax, nmax);
	if (dmin <= dmax)
	{
		dnum = dmax - dmin + 1;
	}

	cout << pnum + nnum - dnum << endl;
	
	return 0;

}
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define MV 200001
#define LMV 21
#define ff first
#define ss second
#define pb push_back
#define eb emplace_back
#define emp emplace
#define mp make_pair
#define ins insert
#define sz(x) (int)x.size()
#define whoami(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); whi(_it, args); }

void whi(istream_iterator<string> it) { cerr<<"\n"; }

template<typename T, typename... Args>
void whi(istream_iterator<string> it, T a, Args... args) { cerr<<*it<<" "<<a<<" "; whi(++it, args...); }

void FLASH() {ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);}
void SETF() {cout.ios_base::setf(ios_base::fixed); cerr.ios_base::setf(ios_base::fixed);}
void UNSETF() {cout.ios_base::unsetf(ios_base::fixed); cerr.ios_base::unsetf(ios_base::fixed);}

typedef long long ll;
typedef long double ld;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef pair<PII, int> PPII;
typedef pair<PLL, ll> PPLL;
typedef map<int, int> MII;

const int MOD = 1000000007;
const ll INF = 4e18;

template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;

struct h_llint {
    static uint64_t splitmix64(uint64_t x) {    // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }
    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
}
};

struct h_pair{
    size_t operator()(const PLL&x)const{
        return hash<ll>()(((ll)x.ff)^(((ll)x.ss)<<32));
    }
};

typedef map<ll, ll> MLL;
typedef map<PII, int> MPII;
typedef map<PLL, ll> MPLL;
typedef set<int> SI;
typedef set<ll> SL;
//ordered_set = order_of_key(.)
//ordered_set = find_by_order(.)
typedef ordered_set<int> OSI;
typedef ordered_set<ll> OSL;
typedef ordered_multiset<int> MOSI;
typedef ordered_multiset<ll> MOSL;
typedef unordered_map<ll, int, h_llint> UMLI;
typedef unordered_map<ll, ll, h_llint> UMLL;
typedef unordered_map<PLL, int, h_pair> UMPI;
typedef unordered_map<PLL, ll, h_pair> UMPL;

int ar[MV];
ll arr[MV];

void solve(int T)
{
    ll b,c;
    cin>>b>>c;
    VL cst(2);
    cst[0] = c;
    cst[1] = c-1;
    vector<PLL> af(2);
    auto rpt = [ & ](int yt){
        if(cst[yt] & 1)
        {
            af[yt].ff = -b-(cst[yt]>>1LL);
            af[yt].ss = -b+(cst[yt]>>1LL);
        }
        else
        {
            af[yt].ff = b-(cst[yt]>>1LL);
            af[yt].ss = max(b, b+(cst[yt]>>1LL)-1);
        }
        return;
    };
    ll ans = 0, iaf = -INF, ias = INF;
    for(auto _=0;_<2;_++)
    {
        rpt(_);
        ans += (af[_].ss - af[_].ff + 1);
        iaf = max(iaf, af[_].ff);
        ias = min(ias, af[_].ss);
    }    
    ans -= max(0LL, (ias - iaf + 1));
    cout<<ans<<"\n";
    return;
}

int main(void)
{
    FLASH();
    //freopen("cowjog.in", "r", stdin);
    //freopen("cowjog.out", "w", stdout);
    int T;
    T = 1;

#ifndef ONLINE_JUDGE
    time_t time_t1, time_t2;
    time_t1 = clock();
#endif

    //cin>>T;
    while(T--)
    solve(T);

#ifndef ONLINE_JUDGE
    time_t2 = clock();
    SETF();
    cerr<<"Time taken: "<<setprecision(7)<<(time_t2 - time_t1)/(double)CLOCKS_PER_SEC<<"\n";
    UNSETF();
#endif

    return 0;
}