program sample
    implicit none
    real(8)::x,y,z
    integer(8) :: a,b,c,i,j,m,n,k,a1,b1,c1
    
    
  
    read(*,*) n

    if (mod(n*100,108)==0)then
        write(*,*) n*100/108
    else 
        a=1+int(n/1.08)
        if (a<(n+1)/1.08)then
            write(*,*)a
        else
            write(*,*)':('
        end if
    end if
    stop
end program sample
  

