#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define INF 1000000000
#define mod 1000000007
using ll=long long;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2")
#pragma GCC optimize("O3")

// おいおい

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    ll n,k;cin>>n>>k;
    ll ans=0;
    rep(i,n){
        if(i%2==k%2 and i<=k) ans++;
        else if((n-i)%2==k%2 and (n-i)<=k) ans++;
    }
    cout<<ans<<endl;
    return 0;
}