#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
int main() {
  ll n, k;
  cin >> n >> k;
  ll ans = 0;
  if(n % 2 == 0) {
    ans += (min(n, k) + 1) / 2;
    if(n % 2 != 0 || n > k * 2) {
      ans += min(n, k + 2) / 2;
    }
    if(n - k <= k) {
      ans = n / 2;
    }
  } else {
    ans += (min(n, k) + 1) / 2;
    if(n % 2 != 0 || n > k * 2) {
      ans = min(n, ans + (k + 2) / 2);
    }
  }
  cout << ans << endl;
  return 0;
}