#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef long long ll; typedef unsigned long long ull; static const double EPS = 1e-8; static const double PI = 4.0 * atan(1.0); static const double PI2 = 8.0 * atan(1.0); #define REP(i,n) for(int i=0;i<(int)n;++i) #define ALL(c) (c).begin(),(c).end() #define CLEAR(v) memset(v,0,sizeof(v)) #define MP(a,b) make_pair((a),(b)) #define ABS(a) ((a)>0?(a):-(a)) #define FOR(i,s,n) for(int i=s;i<(int)n;++i) int main(int argc, char **argv) { ll n, k; cin >> n >> k; if (k == 0 || k > n) cout << 0 << endl; else if (k * 2 - 1 == n) cout << (n - 1) << endl; else cout << (n - 2) << endl; return 0; }