#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
const ll N=1000005;
const ll inf=1e18;

ull seg_len(ll l,ll r)
{
    if(l>r) return 0ULL;
    return (ull)(r-l)+1ULL;
}

void solve()
{
    //freopen(".inp","r",stdin);
    //freopen(".out","w",stdout);
    ll n,m;
    cin>>n>>m;
    if(m==0)
    {
        cout<<1<<"\n";
        return;
    }
    ll l1=n-(m/2);
    ll r1;
    if(m>=2) r1=n+((m-2)/2);
    else r1=n;

    ll half=(m-1)/2;
    ll l2=-(n+half);
    ll r2=-n+half;

    ull len1=seg_len(l1,r1);
    ull len2=seg_len(l2,r2);

    ll il=max(l1,l2);
    ll ir=min(r1,r2);
    ull inter=seg_len(il,ir);

    ull ans=len1+len2-inter;
    cout<<ans<<"\n";
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    solve();
}