#include<bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,n) for(int i=1;i<n;i++)
#define all(v) v.begin(),v.end()
#define P pair<int,int>
#define len(s) (int)s.size()
#define pb push_back

template<class T> inline bool chmin(T &a, T b){
	if(a>b){a=b;return true;}
	return false;
}
template<class T> inline bool chmax(T &a, T b){
	if(a<b){a=b;return true;}
	return false;
}
constexpr int mod = 998244353;
constexpr int inf = 3e18;


signed main(){
	cin.tie(0);ios::sync_with_stdio(false);
	int N,K;cin>>N>>K;
	if(N%2){
		cout<<min(N,(2*K+1)/2+1)<<endl;
	}else {
		int l=1+K+1,r=(1+N)-K-1;
		int n=N-max(0ll,r-l+1);
		cout<<(n+1)/2<<endl;
	}
}