package main import ( "fmt" "log" ) func main() { log.SetFlags(log.Lshortfile) var N, K int fmt.Scan(&N, &K) var ans int if K == 0 || K > N { ans = 0 } else if N%2 == 1 && N/2 == K-1 { ans = N - 1 } else { ans = N - 2 } fmt.Println(ans) }