long recursin(int);

void main()

{

    int n;

    long result;

    printf("input a integer number: \n");

    scanf("%d", &n);

    result = recursin(n);

    printf("%d! = %ld\n", n, result);

}

long recursin(int n)

{

    long temp_result;

    if(n<)

    {

        printf("n<0, input error!\n");

    }

    else if(n ==  || n == )

    {

        temp_result = ;

    }

    else

    {

        temp_result = recursin(n-) * n;

    }

    return temp_result;

}