program factorial
    implicit none
    integer::i,n,factor
    
    print *, "input the limit to calculate factoriel of numbers from 2 ~ limit:"
    read *,n
    if (n<2) then
        print *,'the number is less than 2.'
    else
        factor = 1
        do i =2,n
            factor = factor*i
            print*,i,'!=',factor
        end do
    end if
end program factorial