/CODEN - Cột Đèn

              uses Crt;
        Var a,b,r,m,n,c,d:int64;
        begin
        
          readln(a,b);
          //writeln(a div b);
          //writeln(a mod b);
                m:=a mod 2;
                n:=b mod 2;
                c:=(a-m)*(b-n);
                d:=(a*b)-c;
                writeln(c div 4+d div 2+d mod 2);
        
        
          readln;
        end.