integer n
read *,n

	call fact(n,ifact)
print 100,ifact
100	format("fakt=",I10)  
end


subroutine fact(n,ifact)
if(n.lt.0)then
print *,"n on neg."
stop
endif

if(n.eq.0)then
ifact=1
return 
endif

ifact=1
do i=2,n
ifact=ifact*i
enddo

return
end