program golf
integer i,j,K,A,B
read(*,*) K
read(*,*) A, B
i=0
j=0
if(B-A>=K) then
	j=j+1
else
	do i=0, B-A
	    if(mod(A+i,K)==0) then
        	j+=1
            exit
        end if
    end do
    if(j==1) then
    	write(*,*) "OK"
	else
    	write(*,*) "NG"
    end if
end if
end program
