#include #define FOR(i, a, b) for (ll i = (a); i < (b); i++) #define RFOR(i, a, b) for (ll i = (b)-1; i >= (a); i--) #define rep(i, n) for (ll i = 0; i < (n); i++) #define rep1(i, n) for (ll i = 1; i <= (n); i++) #define rrep(i, n) for (ll i = (n)-1; i >= 0; i--) #define pb push_back #define mp make_pair #define fst first #define snd second #define show(x) cout << #x << " = " << x << endl #define chmin(x, y) x = min(x, y) #define chmax(x, y) x = max(x, y) #define pii pair #define vi vector using namespace std; template ostream& operator<<(ostream& o, const pair& p) { return o << "(" << p.first << "," << p.second << ")"; } template ostream& operator<<(ostream& o, const vector& vc) { o << "sz = " << vc.size() << endl << "["; for (const T& v : vc) o << v << ","; o << "]"; return o; } using ll = long long; constexpr ll MOD = 1000000007; int main() { ll n, k; cin >> n >> k; if (k == 0 or k > n) { cout << 0 << endl; return 0; } if (n == k * 2 - 1) { cout << n - 1 << endl; return 0; } cout << n - 2 << endl; return 0; }