import scala.io.StdIn;
object Solution {
  def main(args : Array[String]) = {
    val Array(n,m) = StdIn.readLine().split(" ").map(_.toInt);

    var count : Long = 0;

    doCut(n,m)

    def doCut(x : Long, y : Long) : Int = {
      if( x ==1 &&  y ==1) 0
      else {
        if(x >= y) {
          count += y
          doCut(x-1,y)
        }
        else {
          count += x
          doCut(x, y-1)

        }
      }
    }
    print(count)

  }

}