#include #define FOR(i,a,b) for (int i=(a);i<(b);i++) #define FORR(i,a,b) for (int i=(a);i>=(b);i--) #define pb push_back using namespace std; typedef long long ll; typedef pair pii; typedef vector vi; typedef set si; const int inf = 1e9; const int mod = 1e9+7; main(){ cin.tie(0); ios::sync_with_stdio(false); int n, k; cin >> n >> k; cout << ((k < 1||k>n)?0:(k*2-1==n)?n-1:n-2) << endl; return 0; }