recursive function gcd(a,b) result(c)
  integer*8::a,b,c
  if(b.eq.0) then
     c = a
  else
     c = gcd(b,MOD(a,b))
  end if
end function gcd
function lcm(a,b) result(c)
  interface
     recursive function gcd(a,b) result(c)
       integer*8::a,b,c
     end function gcd
  end interface
  integer*8::a,b,c
  c = (a*b)/gcd(a,b)
end function lcm

program main
  implicit none
  interface
     function lcm(a,b) result(c)
       integer*8::a,b,c
     end function lcm
  end interface

  integer*8::N,D,tmp,i
  read *,N,D

  print '(i0)', lcm(N,D)/D-1
end program main