program main
	implicit none
    integer::a,b,c,d,i
    real::x,y
    read(*,*)a,b
    c=-1
    do i=1000,1,-1
    	if (int(i*0.08)==a .and. int(i*0.1)==b)then
            c=i
        end if
    end do
    
    write(*,*) c
    stop
end program main